Should I lie to my friend?

Basically, last week I was diagnosed with depression and soon I'm supposed to be starting cbt. I haven't self harmed for quite a while but one of my friends saw some old scars and told my bff. My bff told me what she said but I just laughed it off and she seemed relieved didn't think anything was wrong. I'm worried about seeing the friend that saw it because none of my friends know how I've been feeling. Should I tell her that I'm fine or just leave it because I don't want to tell her the truth but if anyone looks closely, the scars are still there.