Groupon deal! $39 for a month of unlimited boxing classes

Fantastic deal on a month of unlimited boxing classes for $39. Mom said she doesnt want to pay for it as an early xmas gift if I am not going to use it. How do I work it out so that I have something to lose by not going 3x a week? I an thinking I get one free miss then I have to pay her back a little for everytime I don't go. Any other ideas to keep me motivated? I am thinking my scheduled days to go will be Tuesday, Thursday and Saturday