I'm not an expert but I took my grip off, split a 4" long 3/8" diameter wood dowel in half, and glued it to the back of the riser, then wrapped it with camo moleskin. It really helped tighten my groups! I think it helps reduce the torque applied by your grip. Keep your grip as open as possible.
If your shooting to the left, did you move your sight to the left to correct it?