You cannot make changes to a return that is in pending or to a return that has just been accepted.
We do not know if entering the wrong stimulus amount will delay your refund --- or for how long if it does. The IRS has not offered any guidance yet on how they will handle returns that have incorrect stimulus amounts entered. We all just have to wait and see. You are among many people who were confused and entered incorrect stimulus amounts, or who filed early and then received a check.