TurboTax won't let me efile because I only filled out the injured spouse part and not the innocent spouse part. Is there a way to fix this?

If you're filing for injured spouse relief, you should not file the innocent spouse section. 

Be sure you did NOT fill in any years on the Innocent and Injured Spouse Relief screen.  Those boxes are just for innocent spouse relief.

Please follow these steps to complete Form 8379, Injured Spouse Allocation, which can be filed with your return (or separately):

1. Click on Federal > Other Tax Situations 
2. Scroll down to the Other Tax Forms section and click on the Start/Update box next to Report an injured or innocent spouse claim.  
3. On the Innocent or Injured Spouse Relief screen, click on the Yes box. 
4. Don't make any entries on the next 2 screens -- just click Continue.  [They apply to Innocent Spouse Relief.]
5. On the screen Let's See if You Qualify for Injured Spouse Relief, mark the appropriate state box and click Continue.  
6. On the screen, Tell Us More About Your Situation, mark the appropriate boxes and click Continue.  
7. On the next screen, mark whether you reported your own federal tax withheld on the joint return.
8. The next screen will tell you if you qualify for injured spouse relief.  Mark the radio button to indicate whether you want to file this claim with your 2019 tax return and click Continue.  [You can either file form 8379 along with your tax return, or you can mail it in separately]  
9. Continue through the rest of the interview, entering the requested information

If you're still having a problem e-filing your return you can print Form 8379 and file it by mail.  Then you should be able to e-file your return.

[Edited | 3/26/2020 |  9:35 am PDT]