You are very brave to be asking for some help with this. I can appreciate how unsettling it is to create these scenarios — and to not know where they are coming from.
Your examples are about bad things happening to you or your loved ones. There is something about feeling victimized and then expressing (either in your tears in class or telling your friends) that is important to you. The question may be why you would want others to know about the pain you have created. Three are several possibilities for this, and there is too little information here to figure what might be causing it.
I recommend you tell your parents that you would like to see a therapist. Talking about this in person with someone will help you sort it though more directly. If your parents are not open to bringing you for some therapy, I would let the school counselor know that you are having these troubling thoughts. He or she will be able to help.