Ok, it could be fine. Compression gauges measure differential and are calibrated with a spring mecanism. I have a couple of gauges, one reads 120psi and the other 95psi on the same motor testing it at the same time. So 90psi isn't necessarily a bad motor. If you had access to a known good motor, say a nearly new sled, you could use your gauge to check it and that would tell you if you have one that reads low normally.
Does the machine start easy, both hot and cold? You said that its 90psi on both sides, if it weren't... if it had say 15% variance between cylinders that would also be a sign of something bad.
All of that said, 2200 miles on a 2 stroke is in my opinion a good time to start thinking about re-ringing for maximum performance. But this is an 03 600 we are talking about, not the highest HP motor on the planet. If it starts easy both hot and cold I wouldn't be concerned.
sled_guy