you have had one day out of three years and that is AMAZING. you don't have to start from day 1 again. I have never been a fan on tracking but that's just me..when I put to much emphasis on stopping I just never could. nowadays if I need to acknowledge it I think I have only self harmed once in a year and a half rather than days. I don't know if turning it around like that would be helpful to you.
I don't think you should ignore that it happened. Its ok to acknowledge it. That you slipped up but you have learnt from it or however you want to see it and think of what you can do to prevent it happening again.
I 'slipped' the other day too and at first it seemed such a good idea (and it was such a small slip) but pretty instantly I felt awful. I personally am going to try and remember that next time. I know for me. SH feels attractive at times. I think it will solve everything and obviously it solves nothing just means I have to lie and hide and in turn makes me want to hurt myself more and remembering that is usually enough.
Do you have anyone you can talk to about this stuff? I'm here if you do want to talk. I can't guarantee I will have any answers but sometimes it just feels better to get stuff of your chest.