I got caught by my friends when I was cutting on my wrists and it took them longer to find out when I cut myself on my legs, the only reason they did was because of PE and having to change. I would suggest cutting on your hips where underwear and/or shorts would hide them and/or on your inner thighs. If you decide to do it on your inner thighs, do it very lightly, unless you want a lot of pain, a lot of blood, and a high risk of hurting yourself too much. Please try to seek a little bit of help, you don't have to stop, but maybe don't cut very deep as a start. Lot's of love, some stranger on the internet.