If my ex girlfriend grandma claimed me last year can I get stimulus still??

Your ex GF's grandma?  Did you live with the grandma for the whole year?

If no one can claim you as a dependent for 2020 you can get the stimulus on your 2020 tax return.  

The stimulus check is an advance on a credit you can receive on your 2020 tax return.  If something went wrong or you did not get the stimulus check this year, you can get it when you file your 2020 return in early 2021—if you are eligible.It will end up on line 30 of your 2020 Form 1040.

https://www.irs.gov/newsroom/economic-impact-payment-information-center-topic-j-reconciling-on-your-2020-tax-return

https://www.irs.gov/coronavirus/coronavirus-tax-relief-and-economic-impact-payments-for-individuals-and-families

don't worry about 'last year', just fill out the 2020 tax return and you should see the stimulus on Line 30 if you are eligible.