You would not have qualified for the stimulus in 2018 and 2019 as a non-resident alien. But in 2020 if you are still on your F1 Visa, you can file taxes as a U.S. citizen. The 2020 stimulus is an advance on 2020 taxes and you will be eligible for both years of stimulus payments.
You can also file the 1098-T for the education credits for the courses you took in 2020.
