It's not necessarily draw length but definately check it, even with draw length it comes down to form. I can shoot bows that are overdrawn in length and still not slap my arm, it doesn't mean my form is perfect, I just know how to get around it. You might not be accustom to the brace height if it differs from previous bows and your bow arm might be too straight, wrong wrist position ect...

The best way for us to tell anything isn't by word of mouth but if you could post a pic at full draw many here can get you straightened out.

My buddy shooting his Trykon the other day, same thing..slapping his wrist, I stood behind him, adjusted his form, no more slap...his groups tightened as well.