Toddler refuses to poop in potty

I am currently potty training my very strong willed 3 yr old while taking care of my 3 month old. We started in the summer when he was 2 1/2 and the weekend I officially started my whole family got covid. I was so tired and pregnant after we recovered that we just kind of stopped. He then started preschool and his class does not really help with potty training. We picked back up about a month ago and he now is peeing in the potty regularly with few accidents. If he’s in pull-ups he will go more in his pull-ups then when he is in underwear. He has pooped in the potty a few times but does not like it and now refuses to do it. Me and my husband have tried everything and the tension is only getting worse. He just gets very upset or will just avoid pooping altogether. My fear is that he won’t be able to go to preschool in august because you have to be potty trained in that class. Any tips? Any positive stories?