Sliding to bottom end of bassinet..?

My daughter is constantly scooting her way to the bottom edge of the bassinet insert of the pack n play where she sleeps. Like, she has her feet propped up on the side when she wakes up no matter how high towards the top I start her. It scrunches up her sleep sack too, which makes me nervous. She's only 3 weeks old, but does this mean she should move to the mattress insert??