I am amazed at all the recommendations to start in the middle when machine quilting!
With traditional hand quilting in a hoop, it was advised to start in the middle to work any fullness out to the edges. When hand quilting on a frame, however, quilting was done along an edge and the quilt was rolled as quilting was finished.
With machine quilting, assuming the quilt is well-basted, it is not necessary to start in middle. Especially with straight line quilting, starting at one edge and sewing to the other edge is a well-established technique. Starting in the middle is to be avoided as much as possible because of the problem of burying ends -- which is very time-consuming. It's possible to make several tiny stitches at beginning and end so hand burying thread is not necessary, but these stitches do show. Why bother with this at all when you can bury starts and stops in the edges?
One warning I want to give about straight lines. If the quilt is well-basted and the lines do not cross, you will not have a problem. What is more difficult is when lines cross. If you are going to have straight lines cross in your quilt (as with crosshatching), then I recommend heavily starching the backing fabric before layering. Also recommend spray starching the top before layering. Also recommend using basting spray to join the layers. All of these techniques stabilize the layers so there is much less chance of fabric stretching as you sew. One of the big problems with crossing quilting lines is getting a little pucker or tuck right before you cross a line. This is caused by fabric stretching while you sew.
Since you have already glue basted, I would recommend spray starching the top and backing before quilting. You can do this without pressing. Just lay the quilt on a large sheet on the floor, mist with spray starch, let dry (a fan speeds this up), then apply a few more layers of spray starch to each side. This helps keep the fabric from stretching while you sew.