It's telling me to upgrade to add my student loan interest. What if I don't like the way this turns out and I don't submit? will I still have to pay the $90?

You are using the TurboTax Live Basic edition which is currently free to use.  If you need to upgrade that would be to the Live Deluxe edition at $90.  If you do not need the Live edition which includes CPA support then clear your tax return and start over with the TurboTax Free edition.  If required to upgrade to the Deluxe edition it is only $40.  Or if you are eligible you can use the TurboTax Free File Program.

The TurboTax Free online edition is for very simple tax returns that do not require any other form or schedule other than the Form 1040.  If your tax data requires entry on any other form or schedule then you must upgrade to the Deluxe edition or higher.

If you have not paid for the online edition you are using, have not filed your tax return or registered the Free edition, then you can clear your return and start over with a lower priced edition. Click on Tax Tools on the left side of the program screen while working on the 2020 online tax return. Click on Clear & Start Over.

OR - 

You can use the TurboTax Free File Program - https://freefile.intuit.com/

IRS Free File Program - https://apps.irs.gov/app/freeFile/
If you are eligible you can use the IRS Free File Program delivered by TurboTax which is free to file both a federal and state tax return. The IRS Free File Program delivered by TurboTax edition is a full featured personal tax program and on a separate website from the TurboTax online editions.

To qualify for free 2020 federal and state tax returns with the IRS Free File Program delivered by TurboTax, you'll need to meet at least one of these requirements:

• A maximum 2020 adjusted gross income (AGI) of $39,000; or
• You qualify for the Earned Income Tax Credit (EITC); or
• You served as active duty military (including Reservists and National Guard) with a maximum 2020 AGI of $72,000 (you'll also need a military-issued W-2).

See this TurboTax support FAQ on the Free File Program - https://ttlc.intuit.com/community/choosing-a-product/help/what-is-the-turbotax-free-file-program/00/...

See this TurboTax support FAQ for the difference between the Free File Program and the Free edition - https://ttlc.intuit.com/community/choosing-a-product/help/what-s-the-difference-between-free-file-pr...
And see this TurboTax support FAQ on how to switch to the TurboTax Free File Program - https://ttlc.intuit.com/community/downgrading/help/how-do-i-switch-to-turbotax-free-file-program/00/...