Hi
My Louis was the same. He was 14-15 weeks when we took him for his first walk. Weeks before ,I used to put his collar on every day, just for a few minutes and walk around the house and the garden with him. It's hard not to worry as you wonder if your doing it right etc!!.
Even after getting used to the collar, he didn't like going for walks, he used to hide, stop in the middle of the street and sit down etc. I think it took a long time, maybe a few months, before he was happy going out.
He used to walk really slowly on the way out, but on the way back home he used to practically drag me down the street.
When you think, he had only been used to his home and garden for a long time, going out into the big world must have been pretty scary.
Don't worry, everything will fall into place and you will get there eventually.
Gemma & Louis