Maybe you shouldn't lie. Maybe you should be honest with your mom and therapist about this sort of thing. Will you end up in a hospital, you could. I'm about to go back there, I'm not happy about it but I know I need it. Maybe you could go to a different hospital or something. At least get medication or stabilize medication for a few days. Every now and then, honesty will save you. Trust me, I self-harm (in my own way) and I can honestly tell you that I'm suicidal. I wasn't ready to leave the hospital when I did and I understand that now. I understand that I'm still messed up and a hair trigger away from doing something really impulsive. I'm going back because I'm desperate for help and a way out that doesn't involve breaking my fiance's heart.
Best of luck to you, I hope that you'll get better.