Can you please help me on this one.?

right now i do kickboxing and now i lost pion for the sport and i want to join the gym and my mum knows tht i have enogh money finacially each month to pay for it but she wantsme to do kickboxing because she thinks i will be loner because joining the gymis not really a sociable thing to do and she said tht she will let me go to the gym in the summer but i want to go now and i want to quit kickboxing now and join the gym now because i want to work out and build my body up because i train in wrestling every month can u help meplz what should i say so my mum understands