I think that it is not only possible, but probable that this incident was just a setback.

It is really important however to realize that by asking for reassurance, you are giving fuel to the OCD.

There are some really good truths about the path to overcome OCD and some really difficult ones.

The good is that it is completely beatable. I'm having great success using the most evidence based therapy, which is exposure response prevention.

The difficult is that, well, it is difficult. You have to expose yourself to scary things (either on purpose, or through unplanned exposures like when you hit the stop sign) but then not do the compulsive behaviors (like mental checking as to how hard you hit it or asking others if they think it's ok).

I know how hard it is to do and I know how emotionally salient and how powerful the anxiety is that makes it very hard to not to the compulsive behaviors.

We have to recognize the anxiety as OCD and allow the anxiety to be there until it goes away on it's own. Yes, it's painful. Yes, it works.

Let me know if you'd like to chat on the phone or skype or whatever at some point. I'm in Canada as well.

Edit:

I'm adding an edit to this post because I want to make it clear that asking for reassurance or wanting reassurance is totally normal and I'm not trying to make you feel bad about doing it. I'm not saying that you're failing in any way.

To be honest, if I hit my head against that sign, it would still cause me a lot of anxiety, although I would recognize that a lot of that anxiety was from OCD.

I would tell myself that I'm willing to risk whatever might happen in my attempt to heal and get back to normal life eventually.

I was only trying to emphasize the way to overcome OCD eventually. But there will be certain triggers, like hitting your head, that might be much harder and you might not be ready to deal with in the most appropriate way.
This is why we try to build a hierarchy of triggers and tackle them one by one, as we go up the ladder, everything gets a little easier.

So I totally empathize with your concern over hitting your head and understand why it's so upsetting.