I did that as well

Yeah that's what we were thinking, I was so confused haha thank you ladies :)

I had same issue but just bought one a bit thicker

take the thin matress out and just use ur new one thats wat I did

It does fit snug, the lady at baby bunting helped us choose it too so I thought it would be okay. Thank you :)

I think if the mattress fits snuggly into the bassinet with no room for baby to get little fingers trapped in gaps you should be ok. Companies put warnings like that on their products so if something happens and the baby gets hurt they won't be held liable...