Working Out!

Hello! So I am 17 and a senior in high school and the last time I took a P.E. class was sophomore year. I feel like working out will just boost my happiness and mental health, so I really want to start working out in the morning cause I have the time but for some reason the only thing holding me back is my mom. I feel like if I tell her I want to run in the mornings shes gonna judge me and ask why and tell me Im skinny enough (I'm 5'4 and I weigh about 145lb) How do I just do it and stop worrying?