I don't know any new quilter who didn't spend as much time with her seam ripper as she did with her sewing machine. I'm new, and I'm doing a "Block of the month" and my blocks are supposed to be 12 1/2", and they are averaging between 12 1/4" and 12 3/4", and I'm doing a lot of whining. My Darling Hubby Unit listens patiently, and then quietly notes that my "points" are lining up, my blocks are meeting up correctly, and in fact, my blocks look pretty darn good! So I have a problem with seams. I am not perfect -- yet! I whined to the Quilting Board. They were more sympathetic.
Try getting some graph paper, putting it under your needle, and then moving it so your needle comes down just to the RIGHT of the 1/4" mark. Then use blue painter's tape, or border guards, or whatever you need to mark that "scant 1/4" border" so you are guiding your fabric to exactly the right place under the needle. I was trying to use a 1/4" foot, and it wasn't working. I was too focused on what was happening right at the foot, and not paying attention to how I was feeding the fabric into the needle. And I really needed that "scant" 1/4". My next two blocks came out at 12 1/2", right on. Not perfect blocks, but gee, I was happier.
Becoming a quilter is hard work, or so I've discovered. But there is nothing else in the world that compares with the joy, the creativity, the sheer pleasure in this work. Am I addicted? You bet!
Don't give up! You'll get it!