Hey I was riding my new shortboard this week and it's a little undersized for me I'm 6'3 145lb and my board is 6'3" x 18 1/2 x 2 1/2 but every time I seem to grab a nice wave I can immediately turn and ride closer to the top of the wave or I can go down the wave and go for a bottom turn causing my rail to dig in and I lose speed and bail. How do I fix that?