Stop worrying about this so much. He started potty training VERY young and this is normal. Pottying successfully is developmental, and he's not developmentally THERE yet. You are not correct in saying that it's habit that will be harder to break later. What is correct is that it is a hard habit to LEARN now. It will be easier to get it right later.
Give him incentives, like a sticker program, each day. If he has only one or two accidents a day, he gets a sticker. If he gets a sticker at the end of the day for 3 days, he gets a treat. Show him the calendar, clap and act excited that he has one day with a sticker, then say how nice it will be for tomorrow to get another sticker. If he has more accidents, say to him "Aww honey, I'm sorry you don't get a sticker today. I know you wanted to have dry pants. Let's start over tomorrow." Be positive with him, never fuss, and make a big deal out of earning a sticker.
When he gets 2 days in a row, draw a line between the stickers and draw little hearts on the line. That will help him see the difference in "days-in-a-row" and what doesn't get a treat. Same thing for 3 days in a row. Don't make the treat terribly big or important. Make it something that is fun to do with mommy, like baking cookies or something.
Also, remind him every hour "Do you need to go to the potty?" That makes him think about it, and recognize the need quicker than he normally does.
Good luck,
Dawn