Nap suggestions for 8 week old

We are practicing naps in the crib for him. We go In the dark room, swaddle, sound machine, rock and then place in the crib just Drowsy so he can put himself to sleep and he does. But he will sleep no longer than 30 min, on. The. Dot. Besides going in and rocking him to extend the nap a bit, does anyone have any suggestions to get him to extend the time in the crib even just a little bit?

Also after 30 min he still is tired, as soon as i pick him up and rock he falls right back asleep