I have entered a 1099-Q for qualified educational expenses. I am a full time student However TurboTax is incorrectly making it taxable. Why and how do I fix it?

If your Distribution did not exceed your Qualified Education Expenses then you don't have to enter the information from 1099-Q at all.  But if it did, read on for an explanation about what might trigger taxable income when entering a 1099-Q.

For most qualified education program beneficiaries, the amounts reported on the 1099-Q aren’t reported on a tax return. However, if annual distributions exceed your adjusted qualified education expenses, you may need to report some of the earnings reported in box 2 as income on your tax return and pay an additional 10 percent tax on it as well. Your adjusted expenses are equal to the total of your qualified education expenses minus other tax-free assistance you receive, such as scholarships and Pell grants. For example, suppose your qualified education expenses are $10,000, you receive a $2,000 Pell grant and boxes 1 and 2 of your 1099-Q report a gross distribution of $8,000 and earnings of $1,000.

Box 1 of your 1099-Q will report the total distribution from your education program for the year, regardless of whether the funds are sent directly to the school. Box 2 reports the portion of the distribution that represents account earnings, while Box 3 reports the portion representing the original contribution to the account. In other words, the amount reported in Box 3 must equal Box 1 minus Box 2.

In some cases, your 1099-Q may include the fair market value of the account. Boxes 4 through 6 provide additional information, but they have no impact on whether some of your distributions are reportable on a tax return.

Enter your 1099-Q first, then enter all Education Expenses, including books and room and board, if applicable.  

Here is a TurboTax article that discusses the 1099-Q.

If you know that none of the 1099-Q is taxable, just don't enter it in TurboTax. And none of it is taxable if was all used for qualified expenses.  The interview is long and complicated and, as you now know can lead to mistakes.

On form 1099-Q, instructions to the recipient reads: "Nontaxable distributions from CESAs and QTPs are not required to be reported on your income tax return. You must determine the taxability of any distribution." 

That said, You cannot count tuition and other expenses that were covered by tax free scholarship or used to claim the tuition credit for the exclusion from the taxability of the earnings (interest) on the 529 plan. So, sometimes TT is correctly counting some of the distribution to be taxable.  See full explanation below.  

Qualified Tuition Plans  (QTP 529 Plans) Distributions

It’s complicated.

For 529 plans, there is an “owner” (usually the parent), and a “beneficiary” (usually the student dependent). The "recipient" of the distribution can be either the owner or the beneficiary depending on who the money was sent to. When the money goes directly from the Qualified Tuition Plan (QTP) to the school, the student is the "recipient". The distribution will be reported on IRS form 1099-Q. 
The 1099-Q gets reported on the recipient's return.** The recipient's name & SS# will be on the 1099-Q.
Even though the 1099-Q is going on the student's return, the 1098-T should go on the parent's return, so you can claim the education credit. You can do this because he is your dependent.

You can and should claim the tuition credit before claiming the 529 plan earnings exclusion. The educational expenses he claims for the 1099-Q should be reduced by the amount of educational expenses you claim for the credit.
But be aware, you can not double dip. You cannot count the same tuition money, for the tuition credit,  that gets him an exclusion from the taxability of the earnings (interest) on the 529 plan. Since the credit is more generous; use as much of the tuition as is needed for the credit and the rest for the interest exclusion. Another special rule allows you to claim the tuition credit even though it was "his" money that paid the tuition.
In addition, there is another rule that says the 10% penalty is waived if he was unable to cover the 529 plan withdrawal with educational expenses either because he got scholarships or the expenses were used (by him or the parents) to claim the credits. He'll have to pay tax on the earnings, at his lower tax rate (subject to the “kiddie tax”), but not the penalty.

Total qualified expenses (including room & board) less amounts paid by scholarship less amounts used to claim the Tuition credit equals the amount you can use to claim the earnings exclusion on the 1099-Q. 
Example:
  $10,000 in educational expenses(including room & board)

   -$3000 paid by tax free scholarship***

   -$4000 used to claim the American Opportunity credit

 =$3000 Can be used against the 1099-Q (usually on the student’s return)

Box 1 of the 1099-Q is $5000

Box 2 is $600

3000/5000=60% of the earnings are tax free

60%x600= $360

You have $240 of taxable income (600-360)

**Alternatively; you can just not report the 1099-Q, at all, if your student-beneficiary has sufficient educational expenses, including room & board (even if he lives at home) to cover the distribution. You would still have to do the math to see if there were enough expenses left over for you to claim the tuition credit. Again, you cannot double dip!  When the box 1 amount on form 1099-Q is fully covered by expenses, TurboTax will enter nothing about the 1099-Q on the actual tax forms. But, it will prepare a 1099-Q worksheet for your records, in case of an IRS inquiry.

On form 1099-Q, instructions to the recipient reads: "Nontaxable distributions from CESAs and QTPs are not required to be reported on your income tax return. You must determine the taxability of any distribution." 

***Another alternative is have the student report some of his scholarship as taxable income, to free up some expenses for the 1099-Q and/or tuition credit.