If the prettiest girl in your class talks about going to gyms, that does not mean you should go too. Gym is not just having rigorous exercises, there are a number of things associated with it like diet, timing, and trainer.
Do not force your parents to pay for your gym memberships so that you look attractive as the most popular girl of your class.
Do what is right for you. If you intend to lose weight, start with Yogas and indoor exercises that you can do without paying any gym fees. See how much stamina you can hold for exercises and indoor physical activities. First of all, seek comfort from whatever you do and then switch to strenuous activities.