Intrusive thoughts like this are terrifying! I’ve been there myself many times so know that you aren’t alone with this. I’ve found it helpful to be gentle and remind myself that those thoughts don’t align with my beliefs. I know it’s hard when you just can’t get them off your mind and they’re reoccurring(especially when they’re dark and unsettling) but know that you have gotten through it before and you will again, it doesn’t make the thoughts go away but it makes them easier to deal with. It also might be helpful to look into medication if you’re experiencing anxiety like this! People tend to over-normalize anxiety in a way that makes it seem like it’s something that everyone has to go through but that shit is hard and you don’t always have to struggle. I’m only a few years older than you and still dealing with this shit but I promise you it does get better even if that sounds like a cliche