I think you could add some more. Just be aware of how much "puff" you have in the unquilted parts and make sure you don't push the "puff" to the previous quilting in the ditch. That will create a fold you do not want. This might be easier to control if you are doing free motion quilting, It might be harder to do if you are using a walking foot. I would make a practice sandwich where you stitch squares or whatever pattern you did when you stitched in the ditch. and then add the extra quilting you wanted to do. Long arm quilters often will "stitch in the ditch" to stabilize a quilt and then return and do the free motion feathers or whatever. Just practice a bit first.