NEW GOAL HERE I COME 😍😘

So I'm planning to start exercising more often. but I don't know how to start, and if I should record each day I do it or not. people say I'm already skinny (which I know I am) but I don't want to get skinnier, I want to get healthier because I eat soooo much junk food, but the problem is that I have a high metabolism. so I don't gain weight fast, but my fear is that it will all come to me very quickly and I won't be able to lose it. Any suggestions??