92%, average error 5 miles.
Not bad given that Wyoming was my 3rd state.

Only off by 54 miles, dropping a dang square into the middle of the continent.
I'm not so proud about being unable to place Pennsylvania correctly, though. I have trouble figuring out exactly where its Great Lake coast actually falls. That's embarrassing, because I've driven through it.
Minnesota is a good state to get to start. (Texas would be, too.)
3rd try: 100%, average error 0 miles.

(Had to stop in the middle and deal with family, so I didn't record the time.)
I am particularly proud of placing Nevada correctly without any other states in the western half of the US. I guess I do know where California's corner is.