@KB73
The letter you got had several "possible" reasons the return was stopped and changed and the last bullet point of "math error" (which is what the IRS calls the stimulus calculation on line 30) is the one that affects you and not the others.
All you can do is wait for the department tasked with reviewing these corrections gets around to your return. This department usually only sees a few thousand returns per year and they have been inundated with millions of returns to process. This is what happens when the congress makes a tax law change in late December and another in mid March while the IRS is also tasked with sending out 2 more stimulus payments while still under covid restrictions. Patience will be needed by all again this year.
