Probably there will always be someone you could find you’d be more attracted to, even once you’re married. If you want to define settling that way, then most of us settle.
Settling is choosing to be with someone you don’t really want because you realize you can’t get any better.
What she said.
(How nice to agree with you some time, Flyingfish.

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For example: there is a cute girl in my choir but I have reservations about approaching her. It’s not that I’m afraid of approaching her or anything…there are just certain things about her that bother me a bit. I wonder if approaching her is a form of settling because I feel I could find someone else that I am more attracted to.
You will always be attracted to other women. That’s just something you have to live with. Besides, attraction comes on many levels (e.g. not just physical) and there’s a couple of factors other than attraction that make you want to be or stay with someone. Last but not least, your choices and actions shape your attitudes too, so choosing to be a faithful husband once you’ve married changes you in a way.
Now as for that girl. If you start a relationship with someone who isn’t so great a prospect from your point of view, that’s settling. Especially if you look at it in terms of can you or can’t you get any better, it probably means you’re just reviewing your options. Would be nice to fall in love instead (without switching off your brain, naturally), wouldn’t it?

Don’t yield in to pressure, including the one from the so called biological clock (and you’re not old anyway).
It’s only natural that something bothers you in a girl. I doubt you could find any woman nothing in whom would bother you. There’s always something. Question is, are we going to laugh it off or is it going to bring us down? The answer isn’t always simple because the gravity of the problem isn’t the only factor here. For example, we have our “pet peeves” that peeve us more than some objectively more grave concerns that we’d be more willing to live with for other reasons (e.g. our own familiary with those issues resulting in more understanding). You will need to nail down the problem with the girl and think it over and I seriously suggest you don’t skip this step. It will be far less easy when you get involved.
This said, you can always meet her for a coffee (if she agrees, naturally) and have a conversation without indicating romantic interest or imposing commitment. If you do so, I’d be very careful because it doesn’t seem like you’re starting to develop feelings for her or like it’s personal for some other reasons, as I said, it seems to be just reviewing your options. So you’d better keep a level head and a sober outlook.
By the way, a girl wouldn’t be happy to hear you were settling for her. In fact, you’d be far happier to be able to say, “yes, yes, yes, I want it!” than, “okay, I’ll settle.” Sometimes this requires waiting.