Mouth guard sizing

I have a relatively small mouth and strong gag reflex. I’ve been trying Sisu. I had the smaller 3D and then a small and medium aeroguard. The mediums are too big and I think the small aero covers my back teeth but I can’t get it to fit right from front to back. It’s possible I’m just molding it wrong . The small aero is definitely the most comfortable but I don’t want to skate in a bad fitting guard. I put some pictures just in case I’m molding it wrong