Three Month Old Milestones

Hey everyone! My baby girl just turned 12 weeks today and I’ve been noticing that a lot of babies are lifting their heads on their own during tummy time now. My baby girl is able to keep her head stable on her own when I hold her upright but when it’s tummy time she doesn’t seem like she can lift her head up, she seems to have trouble. Should I be concerned? Or am I overthinking? Is there anything I can do to encourage her to lift her head? I just hope she isn’t behind developmentally.