Potty Training

My son will be 3 at the beginning of April. He has been asking to sit on the potty and has shown the other signs of being ready that they tell you to look for, so we have been doing naked time and potty training since Friday. The issue is that he seems to have trouble releasing his pee when he sits on the potty. He can hold it and hold it. He's had some times over the past few days where he has been able to go and empty his bladder. Other times I know he has to go, but he won't, or he will just let out a few drops or a few small squirts. I've done hands in warm water, water running, having him blow bubbles, tickling him, having him eat while on the potty, drink water while on the potty, watch videos, read books, sing songs, run around and come back (I thought it might get things moving), sit on his potty while I go pee on the big potty, letting him sit on the potty and walking away to give him privacy, etc. I've tried everything I can think of. He is a camel. He can hold it and hold it and hold it.

I don't want to push it if he truly isn't ready, but I also don't want to quit if all he needs is a little more time. We have had some successes over the past few days, so I feel like we could get it if we keep going. I'm afraid I missed our window and that it will just get harder the longer I wait to do this, and that going back to diapers will just confuse him. Any advice?