If you want to improve the look of the stitches on the back, try inserting the needle perpendicular to the quilt top, and not at an angle.
I never really worry about the size of the stitches on the back, so long as they actually show up back there! If the quilting on the front is even, then the back usually will follow too.
It helps when you do the rocking stitch to keep the quilt looser in the frame or hoop - it should look like the cat sat on it. If you make it too tight it's hard to make a stitch and you bend needles.