I'd say you could probably go ahead and do that. In fact, that's a good idea because the more exposure you have for Mod 7 (one that I personally find difficult >_<) early on, the easier it is to understand and apply.
One thing I've been doing for these exams (even though I'm pretty much always at the front of the row) is taking in a wristwatch. It has been incredibly vital, especially for me where I know that I am prone to wasting time if I don't manage it well. The little time it takes to break...
You gotta restrict the domain because what you've drawn is a relation. Restrict f(x) to monotonic increasing/decreasing and that will give you your inverse function.