Try loosening your top tension a little (a half number). I always use a practice piece of fabric & batting to try out my stitches before going to my quilt.
Stitch in the ditch isn't as easy as some would have you believe. Don't worry that some of your stitches are not exactly in the ditch and show through. It happens to everybody, and the recipient of your quilt will never notice it.
Pressing the seams to the side rather than open will give you a stronger seam in the long run. Don't obsess over this either. The more quilts you make, you will develop a style that suits you. And remember, there is more than one way to do everything.
Enjoy the process!