really nice rock work... definitely shim the stand up. dont feel bad bud, atleast the floor is your problem. my carpentry skills suck so the first stand i built and wasted about 20 hours on was not level on the back right side. if i filled my tank up on it would have twisted the tank and blew it out. 3 sides of the stand were level but the back right was about 1/4" low. i just built a new one though and got lucky 