Lots of good suggestions -
Double check your pattern pieces - if you used templates - make sure they are the correct size.
I had bought some plastic templates with the pattern shapes printed on them. Turned out that the "square" was 4-1/2 x 4-5/8 - which explained why my pieces weren't going together very well. I didn't figure that out until the quilt was done, though!!! Hey - I bought it - it should have been perfect, right?
Now I trust myself a lot more than I did then.
Learn and live!