Potty training

My son just turned 3 and we decided to up the effort in getting him fully potty trained. But he has some hesitation about going poop on the potty. He'll ask for a pull up to wear, but I keep encouraging him to use the potty. I'm not trying to force it, and I don't want to make his feelings worse, how do I help normalize it for him? He's gone poop a few times and every time I positively reinforce that he did a good job, but he still acts uncomfortable about it.