I think it looks pretty good, but I would worry about the front corner and babies getting stuck... it looks like a good gap... other than that, it should work pretty decently!
It shouldn't be too hard to glue a short piece to the side or foot to cover that gap. Your other alternative would be to replace the foot altogether with a piece that fits better. "Measure twice, cut once" my Dad always said.
Way to get in there, and get it done!! :up: Tweak it a bit, and you'll have a very useful nest box. You have the first one under your belt now, and it will be smooth sailing from here on.