"TurboTax says that I am qualified for the stimulus check and that I will receive a credit of $1800."
That is true. You are misunderstanding the rules.
Under the CARES Act, if you are claimed, or qualify to be claimed, as a dependent on someone else’s 2019 return you did not receive a stimulus check, in 2020. If you qualified as a dependent for 2019, but will not be for 2020, you will get it in 2021, when you file a 2020 tax return.
On your 2020 return, it's known as a rebate credit, rather than a stimulus payment.
Note that the requirement is not just whether you are actually claimed as a dependent, it's whether you qualify to be claimed as a dependent.
"In essence, the (2019) stimulus check acts as an advance of your 2020 income tax refund. This means when you prepare your 2020 income tax return, there will be a line to include the section 6428 credit (line 30 on the 2020 form 1040). The credit on your 2020 return is subtracted by any amount received as a stimulus check in 2020. If the amount you received as a stimulus check (0 in your case) is less than the credit you are due, the difference will be included as part of your 2020 refund. If you have been overpaid by receiving the stimulus check, however, you will not be required to return any excess amount".
