Flat head confusion…

I’m building up a lot of mum guilt thinking my little boy is getting a flat head.. He sleeps for 8 hours nightly in his swaddle on his back and goes down for naps either in our arms or on his side with supervision. He hates tummy time but he spends hours on end upright on us chatting away with his neck up looking around and giggling, or on our chest pushing himself up hitting all the milestones. BUT I still feel as though his head is getting flat. He spends about 40 mins a day in his bouncer watching mr tumble (and poopin… his lovely routine). Am I being a crazy first time mum or should I do something else?