I was trying to hang a 6' long ceiling shelf, measured roughly 6' found 2 studs, started the project. Then by the time I put the 6' shelf up, I found the studs were not 6' apart, they were 6'6" apart. I then started measure each stud, and found it changed some where in between. What gives? This is in the garage, with 2nd story living space above it.

Because of where it is, it is ideal for me to mount what I wanted, but now I can't, unless I move the whole structure over couple feet, and that also ruins my original plan of mounting 2 shelves in the garage side by side. Help!