I’ve been in the same boat as you before, and let me promise, you’re not pregnant. He didn’t finish, and a couple strokes isn’t goes to get the job done. Plan B is effective the next morning, so you’re fine, just make sure you are in the weight limit.
Don’t drink too much vitamin c, you can hurt yourself. If you really feel like you need to do something right now, wash yourself out, with water, NO soap.
Getting pregnant is harder than people think. You’ll be okay.
When you go get a plan B, get condoms. Remember this feeling and make sure you use them. If you’re worried about someone finding them, get a small box, take them out/throw away the box, and hide them. In a book, under something behind a shelf, etc. But better to have them just in case.
Other then that, take a deep breath. I understand panic sets in, but what’s done is done, and you have next steps you can do.