The biggest secret is that absent significant current (or something stupid like the boat leaving you!), you'd really have to try hard to get lost on a dive. Yes, go out and practice your navigation skills; it will build your confidence and make you a better, self-sufficient diver. On the other hand, if you are comfortable with the safety and life-support aspects of diving, the worst thing that is likely to happen is you can't find the boat while you are under water. OK, so surface and look for it; I doubt its more than a couple hundred feet away, if that. Signal you are okay, go back down and now you know where to go. It hurts the pride when you can't find your way back to the boat submerged, but it's rarely dangerous.