This has happened to me a few times. I've been rooting along thinking im fine until i finally look Inside to see the missing patches and hair hardley poking through!! Ive had to pull all the hair out and start over in those spots bc its way too hard to try and go through each hair to poke in further. I have left one head that was rooted this way and sure enough, after washing and combing through the hair, it just came out. When there's not enough inside and its just poking through a tiny bit, you can't glue the hair down. It just pokes right back up and your not actually gluing it down to anything if that makes sense. If you are just keeping this baby and don't want to deal with pulling it out and re rooting right now, then i would just finish it and glue down what you can and later if the hair comes out you can redo it then if you wanted. Or maybe if your real careful, it will be fine for you. Sorry this has happened, i now root with a rooting light inside the head so i can't see inside unless i take the light out but i now always check inside every so often to make sure the hair is pulling through enough!!