I live in FL, work remotely for a company in CA. I already filed, but just realized on my W2 they've been taking out CA withholding and disability. Can I get refunded?

Yes, if you did not work in California but had CA taxes withheld, you will need to file the CA nonresident tax return to get the money refunded.

See How do I file a nonresident state return? - TurboTax

Thank you!  The only thing is, I've already filed my return. Do you know if there's a way to go back into my return and do these steps through TurboTax?  Or will I now have to do this manually (print the form out, mail it in)?

Yes, you can add the California return.  Follow these steps:

1. Sign in to TurboTax.
2. Under Your tax returns & documents, select Show, and then select 2020.
3. Now select Add a state (this reopens your return).
4. Select State from the left menu (on mobile devices, tap in the upper-left corner to open the menu).
5. On the Let's get your state taxes done right screen, select Continue and follow the instructions.

Because you did not work in California, you will have to indicate zero California source income.  

As a nonresident, you pay tax on your taxable income from California sources.  Sourced income includes, but is not limited to:

• Services performed in California
• Rent from real property located in California
• The sale or transfer of real California property
• Income from a California business, trade or profession