Is my skimboard too small for me?

I weigh 120 lbs and I have a zap medium wedge. When I try to ride it, I plow through the water instead of skimming on top of it. Do I need to upgrade to the large wedge? How do you get enough speed to skim out to a wave? In case you haven't noticed, I'm new to the sport and I would appreciate any tips or suggestions you have. Thanks!