Since you pinned, be sure to remove pins as you come to them when you machine quilt.
One of your biggest problems with straight lines is to make sure you don't get puckers and tucks, both on the underside and on the top. This is especially the case with cross-hatching, since you will be crossing lines. Fabric tends to bunch up so you get a little pucker right before the line cross. The temptation is to stretch the fabric to avoid the pucker, but this is not good either.
It is easier to prevent puckers if you heavily starch the backing (and spray starch the top) before layering. Since you have already pinned, you may not want to do that. In that case, you can simply lay out your sandwich on a large sheet and spray starch both the top and bottom several times (misting, then letting starch dry before misting another layer on). This will stabilize the fabric so it is less likely to pucker when you cross a line while machine quilting.