If I forgot to put in my 2017 student Loan interest statement when I filed my tax return, Is there still a way I can put it in even tho I've finished my taxes?

If your return has been submitted, you should wait to determine if it has been rejected or accepted.

If rejected, you can go back and change or adjust your return to include your student loan interest..

 If accepted by the IRS, you should wait until you receive your refund or paid your balance due to amend the return.

When you amend, if the result does not make a difference, you can disregard it.

If the result does change, print and mail  the amendment and include your student loan interest statement (it cannot be e-filed) and allow about 16 weeks for processing.

See How Do I Amend a Return Already Filed?