The TF should auto-calibrate, meaning it looks for the highest and lowest positions it sees, and calls these 0% and 100%.
With some pedals, you can get a problem when you hit it hard it can deform a bit and go to a high value which is not encountered in normal use.
My guess is this is what is happening to you – to confirm, power up the unit, then move the pedal gently to both extremes, it should show 0 and 100.
If this is the case, either see if there are any adjustments you can make to the pedal to stop it going "past the end", or, try a different pedal.
