16 week old won’t finish her nap unless she’s held

So my 16 week old (she’ll be 4 months on the 6th) has always been held for her naps. I have been trying to lay her down for nap time recently. She will go down fine but wakes up at 40 minutes EVERY. TIME. I know she’s not done napping because her naps last anywhere from 1 1/2 to 3 hours. I can pick her up and she’ll go back to sleep within a few minutes but if I try to lay her back down she’ll wake up. If I keep holding her she will finish her nap. Any suggestions to get her to take her whole nap without being held?