I filed this years return as someone can claim me as “dependent”, rather than “Independent”. Is it already too late to change this since I filed?

Pretty much.   You can amend----but it takes 4-6 months for the IRS to process an amended return.  So if you are just wanting to amend for the next stimulus check you are unlikely to get it by amending.  You will be able to file correctly on your 2021 return next year and get the 3rd stimulus next year if you cannot be claimed for 2021.

Appreciate the quick response and honesty. Guess it’s my loss at this point haha