@Anonymous From what you are saying about being devastated, about worring if you are misremembering or if you are afraid that you thought it intentionally, is a huge sign that you didn't intentionally think about it. It was intrusive. If you meant it, you wouldn't be so afraid that you did.
Intrusive thoughts are super weird, so it makes sense for you to not make any sense of it. From my experience, intrusive thoughts start as a a flash thought, something you never, ever would even think that you would think about. And then they become something intrusive when you start to think about how awful that thought is.
It feeds on your fear of it. The thought keeps coming back over and over again because of how much you fear it, and your OCD knows how much you fear it.
The reason you are hearing the intrusive voice telling you that you may have done it intentionally, is because OCD likes to keep you in fear. If you are afraid of it, it is allowed to keep sticking around.
Sorry to relate it to a giant monster of sorts, but it's not wrong. It's a giant monster that grows bigger and stronger the more you fear it. You fight it with all of your might, but with every attack it grows even bigger.
In my experience like yours, the thought came barreling forward unwanted and the more that I thought about how I wanted it gone, the more it stuck around. The first thing you have to recognize is that it is an intrusive thought, that it's unwanted and the reason that it's there is because you don't want to think about it. So, fighting it with trying to put it out of your mind won't work because it's just gonna keep sticking around.
I don't know why it works, but for me personally, when I have an intrusive thought I make a ticking noise three times with my tongue. It might be that I spend enough time listening to the ticking, or that it tricks my brain for just a second and the thought is kept at bay. Like a forcefield. I know some people who view the thought as a angsty teen who is just trying to get attention, and when thought of like that, it's more dismissive of the thought and it leaves. The trick is to not give it any power, to dismiss it, and that may look different for everyone and it is definitely easier said than done.
I hope this helps you; just remember that you are not a bad person, you just have bad OCD.