Four month old baby

So my baby is four months old. She was born at 36 weeks, so the dr try’s to give her some leeway with meeting milestones. At her four month check up her dr mentioned her always holding her thumbs against her palm. She doesn’t use them to pick things up or anything. Her dr said she’d contact help me grow to get her seen by a therapist for it. They haven’t called me yet or anything. I’m starting to freak out and feel like it’s my fault that she doesn’t use her thumbs, especially since she can’t fully sit on her own yet and falls forward a lot. I feel like maybe I missed something these last four months to help her grow and learn new things. Has anyone else’s child done this and them eventually use their thumbs perfectly fine?