Make sure you keep your bow arm up ( follow through ) allowing total execution of the shot......low and left can be a sign of doing the peekaboo thing trying to see your shot. I tell guys to try and see their shot through their peep...not possible, but helps keep the bow up after the shot.
Was it set up by a pro shop ? Center shot and nock point can give the same results.
Your follow through would be the first thing I would check, especially after shooting for that long. Honestly a 2.5 hour practice period is probably going to do more to develop bad habits than good. You'd be much better served by shooting 10 arrows a day, focusing on making each individual shot sequence absolutely perfect. Concentrate on grip, anchor, breathing, surprise release, and follow through.
I don't shoot year round (although I should), and I usually find my first few days my groups may be off slightly. As my form settles back in the groups will come to zero. If not, then I move my sights.
If this is a new bow, your string is still settling in (stretching) so don't worry about tuning for about 2-300 shots.