I keep getting constant nightmares and intrusive thoughts that I'm dead after slitting open my wrist by accident
Why would you have such terrible nightmares?
I'm very scared that I might actually do that to myself
If you feel that strongly, I think that you should go get help! Mental health is just as important as physical health.
I don't want to see people I don't like. If I'm dead that would make happy.
If you think you're better off dead, then I strongly urge you to seek help. There's no reason for you to feel this way!