Baby fell back

Hi, my baby is almost 4 months old and has started sitting for short periods then falls. I usually have my hands ready to catch her, but this time she fell backwards and hit the back of her head on the floor. She was on her playmat, which was also on top of another bigger floor mat which is squishy but not that thick. She cried after she hit her head. Obviously she only fell from a sitting position onto her back, and on 2 soft surfaces, however I’m very anxious about it all. I read online to monitor, and she has been herself since. Happy, playing as usual. There’s no lumps/red marks on her head. Will she be ok or should I keep worrying? I feel like a bad mum but I know these things will happen. Please let me know if you’ve experienced anything similar.