A few things can show left hits (for righthand shooters), but the easiest to say is spine. If it were me, I'd be shooting 2018's off that rig. Other things to keep an eye on -- nock fit (can't be too tight), and anchor and bow arm. Drop the arm after the shot and hits will end left. You can try to add some weight up front to have the arrow show weaker...try 200 or more grs.
You can do some searches here for "arrows hitting left" and you will likely get a days worth of reading.
Also, plenty of guys would love to consitantly group 3"s left, not too bad and should be easy to correct with some of the above.