Next you want to top-stitch all around the top. Before you start sewing reach inside and make sure the seam is pushed out all around. Then pin your opening closed being sure to fold in all the raw edges and top stitch around. You can kinda pull the lining more to the inside while stitching if you want to make it look a little nicer.
Once you have the stitching in place, cut out your handle about 1/4" from the stitching line.
And that's it! Enjoy your new bag! Here's the inside of mine with my computer & accessories.