When I first started machine quilting, I would always draw a pattern on the quilt. As I made more quilts, I got more comfortable with quilting without the pattern. My first FMQ quilts were just meanders, and I look at them now and see uneven stitching, bad tension, and just mistakes- but in order to get where you want to be as a quilter, you just have to keep at it. I'm still not where I want to be, but I'm a lot better than I used to be, and I know I'll keep improving with every quilt I make.
If people quit making quilts because every quilt is not perfect, there would be a lot fewer quilts around.
And lastly, some people are just better at piecing, and some are better at quilting. If you just feel like you're not improving, maybe you can pay someone to quilt your quilts, or find someone who'll trade quilting for piecing with you. I've actually thought about it, because, while I enjoy piecing, I really love FMQ, and I'm a better quilter than I am a piecer.