When Scott wakes up and tries to start his truck, the fuel gauge needle can clearly be seen showing a full tank. In the next seen after the truck won't start - a second or two later - the needle is on empty.
Ohio has class football. Coldwater would never meet the large school in the playoffs. Also, soybeans have been a common crop grown in Ohio, long before 1991.
The 1991 Michigan-Ohio State game was played at Michigan Stadium. It was the Desmond Howard "Hello Heisman" punt return game won by Michigan 31-3.
When Scott goes back in time, his truck mirrors are small and while he is driving they keep changing size.
When Scott wakes up in his old truck. If the engine runs out of gas the ignition light will come on. when the camera pans to the cluster, the ignition light is off.
When the football game is about to happen they show the town and there is a 2007 Impala in the parking lot.
When Scott has gone back in time, and sees his Mom for the first time outside of the trailer they live in, the temperature gauge on the wall indicates that the outside temp is almost 100 degrees. This is supposed to take place in Northwest Ohio in the late fall (a sign with a 419 area code gave that away). Temperature average in Northwest Ohio in the late fall is about 72 degrees.