Nap Advice

My daughter will be 12 weeks old tomorrow. She had colic (finally growing out of it) so has only ever taken naps while being held because we were just trying to survive. She sleeps just fine on her own at night, she’ll go 3-5 hours before waking to eat. But if I set her down for naps she’ll only sleep 20 minutes at most anyone have any advice on how to get her used to napping on her own so that she’ll sleep longer. I’m already trying a shortened version of our bedtime routine.