My baby was closer to 6 months before rolling over, mummy 😊 My PD wasn't concerned because she had good head control and was meeting her other milestones. The scooting/pushing with her legs sounds like she's figuring out how to move around too 😅
As for sitting, I did lots of supported sitting and floor play around that age, but I didn't force it. Most babies will develop the strength gradually. ❤️