Bought a bad bike need help
So I have been shopping for a bike. Ended up with a trek 7.3fx. Seemed like a great overall bike as all I am doing is commuting. First day I get it the chain has or developed a pinch/scratch in one of the pins which caused the chain to constantly jump on the rear gears. Go take it in and they replace the chain. Today I get it back and ride for maybe 1.5mins and as I am riding up hill I switch to a lower gear on the front gearset. Well the chain then lodges in between those gears and I almost go off the bike because of it. So now I have a chain that is wedged in between the gears and will not budge for anything. Looks like I will be taking it back but I think this time going to return the bike because this is just nuts.
What I need help in is being over weight, 245 6'1", am I the complete cause of these problems? I know I my weight does not help anything but now I am almost nervous to ride the bike in fear something else is going to break. Should I just have the fix it or should I return it and get a sturdier bikes? I feel like for $550 I can get something much sturdier. Any help would be really appreciated. Thanks.