I marked that I can be claimed on someone else’s taxes but was not claimed. Can I amend my 2019 tax return and receive the stimulus

[DanielV01]

At this point that is not necessary, nor will it resolve your situation.  However, the stimulus payment is actually based on your 2020 filing status.  So if you are not a dependent filer in 2020 (which you will be filing this year), you will be able to retro-actively claim the stimulus payment, and it will be added to your refund amount.

[Mike9241]

it doesn't matter whether that if someone could claim you as a dependent but does not.  you must mark the return that you could be claimed.