SSA 1099 box 5 says to enter the net SS benefit. However, the SS 1099 actually has the gross benefit in box 5 including the amt. pd. for Medicare ... is this an error?

No, it's not an error. The "Net Benefits" in box 5 is just the net after subtracting any repayment. As it says in box 5, it is the total benefits in box 3 minus any repayment in box 4.

The amount in box 5 is the net amount that Social Security paid out, after accounting for any repayment. It's not supposed to be the amount you actually received. The fact that some of what they paid went towards your Medicare premiums does not change the fact that they paid it. The Medicare premiums are not supposed to be subtracted from box 5. It's the same as if they sent you the full amount and you wrote a check to Medicare.

You enter the amount in box 5 in TurboTax.