Check that you have the max amount of $7500 in the box that says "Credit Amount." That box is NOT for the amount you expect to receive. If that box says $3750 and you are in a phaseout period, you will get a reduced credit.
If you read the rest of this thread, you'll see some discussion on that box. I feel that it's not at all intuitive what it's purpose is. It tripped me up for quite a while as I was putting in my Model 3 info.
