Ok, so I've been in this situation. It's a very common queer scenario to feel guilty for having feelings for someone, so I can relate, but it can happen in other situations too, specially when you feel unwanted or like it's way too much of a long shot.
So there are several things to be considered. First off, it's totally okay to like someone, as long as you're not disrespecting them in any way. Your feelings are valid, and obviously intense. But you should also consider certain things, like if you ever make her uncomfortable, or stare at her too much, etc. It may be something you don't realize, but sometimes when you tell someone how you feel about them you can be putting them in a difficult situation as well.
So, basically, I don't think you should apologize for liking her, but if you feel like it put her in an awkward situation, maybe it'd be a good idea to apologize for that. If you feel like she wants space, it'd be wise to respect that and try to get your mind off of it. Try to always do what you feel is adequate.
But don't beat yourself up, regardless of what happens, ok? It's okay to be confident about yourself. Sometimes being different is what makes you extraordinarily gifted, you just have to find your way to express it. I hope this helped you!