Could be spine, could be form, could be the bow. What are you using for a bow...arrows? If your bow is not cut to center, spine is much more critical, but your form can also effect it. I know this because...
My Kota is not cut to center, so I had to learn to adjust. My arrows were not too stiff, but acted just like yours--small groups high, left. I opened my stance a bit, rotated my string hand out (right for a righty) and made sure my eye was looking directly down the arrow. Bingo!
I still drift a shot left if I forget to do any of the above, but it is becoming rarer. I shoot cedar arrows 50-55 spine cut to 29" BOP with 125 gr. points. I tried them at 30 and 31, which didn't help, so I was sure spine was not the issue.
If your arrow flight is good, give these things a try.
Russ