I would try another day of no pants, to help cement the progress you have made. And when he’s at nursery, see if they can take him to the toilet every hour and help him with his undies to try to build that new routine/association there
He might not be ready yet lovely. But also it takes longer than 2 days for them to learn especially when underwear is confusing for them. It can take a few weeks and longer, especially if not ready so just keep it in mind is all. I'd send him in pull ups or something for nursery, explain you've been potty training and they should be able to help support you and take him to the toilet etc but chances are it's going to be hit and miss. Sarah Ockwell Smith has a guide to gentle potty training, I'd recommend that. I've also heard good things about the oh crap book/method but also it's been controversial so all depends how you align in parenting really! Xx
We have been slow potty training for months (I didn't really know what to do and I thought that was the norm 😂). He is successful now when he is free range at home but as soon as the underpants go on he just goes in them! He still goes to nursery in his pull up nappies but they are quite good at encouraging him to use the toilet and letting them know if he needs to go.
Keep his free of underwear for longer. Even if you need to do go just put him in loose shorts so they don’t feel like a nappy.