Good advice to call the Samaritans.
i don’t know if this will help but having negative and self critical thoughts is very human. As cave dwellers we were better off in tribes and of course we had more chance of survival if we were on the lookout for what can go wrong. This is your brain looking out for what could go wrong. How that looks is different for everyone but the themes are often about not being good enough, not fitting in, messing things up. Thoughts of harm to self are actually more common than we think.
Take some deep breaths and ground yourself. If you don’t know any grounding techniques yet then a quick one is to count the different colours you can see in the room, including shades of the same colour. Keep breathing, have a shower, get dressed, have some breakfast and head out to your job. If you feel panicky breathe well. This links to a breathing video to help slow your breath.
https://nopanic.org.uk/important-breathe-properly-help-anxiety/
This job matters to you, so try to notice the thoughts and feelings that are coming up, but keep doing what matters.
What would you say to a close friend in this same situation? Try and be compassionate towards yourself. You are human. You are doing your best. You are not, nor will you ever be, perfect. You are unique and flawed, just like everyone else. You might have a bit more work to do, to maintain balance and achieve a level of wellbeing, but it’s absolutely possible.
In terms of self harm, make sure any wounds are cleaned so you don’t get an infection. This is a good time (of life) to try and find some alternative coping strategies. You’ll probably learn some in your new job but get a head start and look up ‘distress tolerance’ skills and ‘emotional regulation’ skills from DBT (Dialectical Behaviour Therapy).
Congratulations on getting the job and good luck. 💐