Presumably, the difference between the urologist's rooms and your home is that at home this procedure has sexual overtones (which is to say, you develop a little erection) and at the doctor's, it just doesn't! That is really the only plausible difference I can imagine to explain your difficulty (but read the following posts referenced to understand how to deal with "
paraphimosis").
I suspect you haven't taken the important first step of using this "forum", which is to
read previous answers and locate the important information which is so often given. Please do this and do some of the stretching recommended rather than worry about "
paraphimosis". That is, until you have actually
stretched your foreskin to loosen it, perhaps you would actually be better off not to try and retract it.
On the other hand, perhaps you
could give us a little background of roughly how old you are, what experiences you have had with this particular "problem" including whether it has actually proven to be any sort of "problem" at all, or how you might expect it to be?
You
are particularly lucky to be in a country with competent urologists.