Dear Jenny - Tummy Gap
Often you get a gape at the front when the back is much higher that then front. Ensure when you put the nappy on that you pull the front panel up towards the belly button to secure it so its in line with the back of the nappy and sitting flat across the tummy. A small gap is normal and gives bub comfort when going from flat to upright.
If this doesnt help please send me a photo so I can check your fit.