Worried about head control/head lag

My 15 week old baby has been doing really well with all of his little milestones. He is pretty good with tummy time and has been rolling over for a couple of weeks (tummy to back) in a very controlled way. He is very smiley, makes so many noises and is starting to grasp for objects and will grip and shake them as well. However I’m now concerned about his head/neck control. I didn’t know about the pull to sit exercise and tried it out and he has major head lag. He doesn’t even attempt to tuck his chin in until at least 3/4 of the way up. The Instagram account milestonesandmotherhood has a safer version of the exercise where you hold him by his shoulders instead of his hands. Anyway, I’m now working on practicing that but from what I read they should be able to do it by 3-4 months, if not sooner, and my little guy will be 4 months in a couple of weeks and he’s not even close. When I google it’s scary what comes up- I know I shouldn’t. I will be sure to ask my paediatrician at his 4 month check up but does anyone else have experience with this? Should I be concerned or could he just be behind in this one area?