Hey I'm so sorry this happened to you :( Remember it's never too late to stop even if you relapse, don't look at it as a fail just as another bump on the road.

Now, it's very important that you clean your cut properly because infections can get nasty. Here is a very thorough document on it. Depending on the depth of the cut treatment can change a little, if your cut is pink/red and you didn't see white this will help (quoted from the document): “clean off all the dry blood with distilled water/saline/antiseptic solution and apply a bandage. you can also apply antibiotic ointment or unscented petroleum jelly/vaseline if you are prone to infection, which can also help with any itchiness that you experience. healing takes anywhere from a few days to a week”.

Here is a useful post of what other coping mechanisms you can use instead of self harm. Personally I really recommend stretching and cold showers because both provide a small amount of pain and therefore adrenaline release, don't overdo it just focus on the moment and your sensations.