Your perfectly fine. Travis Turner (from Realtree) was on Monster Bucks 11 hunting out of one, and he is supposed to weigh right around 500 pounds.

Your stand has a 350# rating, but you have to take into account that "safety standars" are usually tested to 3 times the amount that they are rated. That stand probablly had 1050 pounds on it without any major malfunctions!