I just want to pop in and say a few things to you as Plan B/Ella/other types of emergency contraception.
Did you know they work the exact same way as regular birth control pills? In other words, there really is no difference between using Plan B and taking the pill every day (or using the patch or ring). They work the same way and do the exact same things to prevent pregnancy. Just like the withdrawal method is a method of contraception, so is Plan B. Either way, you're doing things to disrupt what might normally happen with intercourse in order to keep pregnancy from being a result.
If you aren't ready to be a parent or to be pregnant, don't want to be pregnant or a parent, or want those things but know the time or the circumstances aren't right, then using one or more methods of contraception is the right thing to do. You didn't do a bad thing here.
Too, withdrawal all by itself really isn't a great method of contraception. In typical use, it's one of the least effective. Your concerns about this are not only okay to have, they're sound. If you absolutely don't want to be pregnant, just using withdrawal wouldn't have been very smart. This isn't about trust, it's about biology, you know?
I do also want to say that if, at any time in your life, like more than half of all people who have the ability to become pregnant do, you want to do more than use birth control to keep from being a parent -- if you want to choose abortion -- that is a completely acceptable choice. You get to feel however you might feel about that, in that event, but choosing abortion isn't a bad thing -- it's often a very responsible choice as well as one that's very much in the interest of basic self-care -- nor is it anything anyone who has chosen to use or will choose in the future should feel bad about. <3
(Per the "floating sperm," they're just cells, not probably the cartoon beings you might be imagining. Just like you have blood cells in your body, and skin cells in your body, and bacteria in your body, there can be sperm cells in your body. But I hear you, if any of this is new to you, I'm sure it seems super weird.)
Never doubt that a small group of thoughtful, committed citizens can change the world. Indeed, it is the only thing that ever has. - Margaret Mead