Baby won’t nap when out

Last week for the first time, I met a friend for coffee and my 3.5 month old baby just started being extremely fussy during the outing. It was my baby’s usual nap time and I couldn’t get him to fall asleep. After trying to soothe him for 20 min and failing, I felt very stressed and decided to go home. My friend absolutely didn’t mind but I just felt so stressed.

How can i get my baby to nap when im out? I feel trapped inside the house