Starting to machine quilt my very first quilt! I got one edge done and then stopped because I don't know if I should go around the parameter or just continue in rows across the quilt? I'm not doing any fancy design, just a zigzag stitch. I don't want to mess my quilt up after all this work, so how should I go about finishing to prevent bunching?

PS: I have it all pinned and used basting adhesive (can't be too careful!).