Hi Lee,

Your not doing anything wrong - this is the only problem with a one size nappy without a one size insert, they work fantastically on the small setting with the small insert and great with the large or both on the large setting but the medium setting is a PITA. A couple of thiings you can try
- use just the small insert
- use both but instead of snapping them together place them on top of eachother, folding the larger insert over a bit in the front making the length shorter
-use a one size insert like the cottonbabies or jamtots

HTH :-)