I totally get the lack of motivation from a non-structured gym experience. I have joined gyms many times over the years only to drop the membership because of lack of inspiration. It is one of the reasons why I am such a CrossFit nut - it is basically total bootcamp gym. You go there, do what they tell you to do, and crawl home
I guess my response depends somewhat on what your goals are. But if the bootcamp strikes a chord, I am totally with Abby on this. Check with the instructor (or someone in the management team) to make sure of the intended fitness level; I'm guessing it is intended for all fitness levels, too. Then jump in. If you don't like it I bet you can change classes later.
Although I have never done Zumba, I did really enjoy a jazzercise-type class many years ago. It was a fun way to burn some calories. But if you really want to get in shape quickly, I am betting the bootcamp is just what you are looking for.
And, yes there will probably be folks fitter than you, but they all started somewhere, ya know? and most will be super supportive of your progress.