I marked that I can be claimed as a dependent on my taxes, but was not claimed. This in turn is making me seem uneligable for the stimulus money

Indicating that you can be claimed by someone else (whether they actually claim you or not) will disqualify you from receiving a stimulus payment.  If you have already filed your tax return, you would need to amend it to make that change.   If you have not filed yet, you can update your tax return to indicate no one else can claim you.  

The stimulus payment is a tax credit for the tax year 2020.  If you qualify for a stimulus payment (no one else claims you) and you do not receive a stimulus payment this year or before you file next year - you will receive it with your 2020 tax refund.  You won't lose it if you qualify for it even if they don't send it to you this year.