This is most often due to a belt that is improperly installed.

Remove both the record, and the slip mat from the turntable. Rotate the platter so that you can see the brass motor spindle through one of the holes in the platter (it should be located in the bottom-left corner of the turntable).

There is a groove in the brass motor spindle that the belt needs to be seated in. If the belt is able to ride up or down on the spindle, so it is wrapped either above or below the groove, the platter will spin too fast.

Reposition the belt so that it is wrapped around the spindle's groove.

If the belt slips out of the groove when the turntable is played, and is able to ride up or down on the spindle, you'll need to adjust the position of the belt on the inner ring of the platter. The inner ring of the platter is quite a bit wider than the belt itself. The belt should wrap around the middle part of the inner ring. If it is wrapped too high or too low around the inner ring, it could cause the other half of the belt to ride up or down on the spindle.