I had the same problem (45 chickens) day 1 - 3 I had to put the chickens in the coop myself. Found a thread on backyard chickens that suggested a light inside the coop. Day 3 with light inside the coop all chickens put themselves into the coop. Same for days 4 - 5 and still going strong. I recommend a light in the coop.
I put a shop light on a smart plug and set the smart plug to come on at 7pm and off at 9pm. worked perfectly.