I don't see anything wrong with it. As you stitch, it will naturally pull the fabric in towards the stitches, but yours doesn't look excessive to me. It is a good idea when stitching long lines to stitch in both directions..stitch one row from one end, then the next row from the opposite end.
If you look at pics of quilting, I think you'll see that yours is about right..keep going, you'll be happier with it as you quilt more of it and see the overall look.