I don't have much of a problem with out-of-square tops after I put them together, but things can change after I wash the quilt.
I like to wash my quilts after I quilt them. I love the look of a crinkled up quilt. Sometimes, though, after I quilt an all-over meandering stitch, the top can get a little longer or shorter on a side or two. In the shrinking process, one side might shrink up more than the other, because of a little more quilting, or who knows what. Anyway, I don't put binding on until after I wash the quilt. Then I use the binding as an evener-upper. If one side is a tiny bit longer than the other, I just ease the quilt to the binding. It doesn't take much, just a little stretching of the binding before sewing it down.
Even though I almost always wash my fabric first before cutting, I like to put the binding fabric in the wash, again, along with the quilt, so I am sure that most of the fabric shrinkage has taken place before I sew it on the quilt.
