A lot depends on who is doing the judging. At our smaller county fair, the judge is not a certified quilt judge, and just about everyone gets a blue ribbon. At our quilt show and our state fair, however, we have a certified judge, and they look at everything: the joins on the binding, the points in the blocks, the quality of the quilting (and our last judge said custom quilting is the way to go - edge-to-edge has its merits for certain quilts, but you don't get as many points as you would for custom), etc. I don't know how much they look at how square the final product is, but if it isn't somewhat square, it will be noticeable and you would likely "lose" points for that. So, just take your time, make each block as square as possible, and - in short - do the very best you can. Even if you don't win a top prize, hopefully the critique of the quilt will be helpful for the next time.