Take advantage of some New Year's Eve party to gain 10 lbs and fatten yourself up.
Honestly, 2cm doesn't matter to a beginner. The extra length just adds a tinge more stability to your ride. Use that stability to bomb past speed control and show em who's boss.
You may want to shorten up if you plan on doing park, but your stepdad should just get you a new board at that stage of your progression.