If I I didn't enter my 1098-T info for my 2017 return (I paid off my remaining tuition during that year), does this affect my return? Could I report it in my 2018 return?

[Texas Roger]

What do you mean by "I paid off my remaining tuition during that year"? Were you in school in 2017 or was that a payment for a prior year when you were in school?

[DoninGA]

You cannot enter a 2017 Form 1098-T on a 2018 tax return.  If you want to enter the 1098-T then you will have to amend the 2017 tax return.  An amended tax return can only be printed and mailed, it cannot be e-filed.

See this TurboTax support FAQ for amending a 2017 tax return - https://ttlc.intuit.com/questions/4252298-how-do-i-amend-a-2017-return-in-turbotax

[ScruffyCurmudgeon]

1. Almost all taxpayers are "cash basis" tax payers meaning in any one year you report income received and deductible expenses paid only in that year.  So, no, if you paid it in 2017, it is not relevant to 2018.
2. As to 2017, did you intend to file for education credits, or any educations expenses, including possible state deductions or credits?  You need to review what you did do and determine if amending the 2017 filing(s) would generate any substantial refund.