You phrase your question as a rational consideration. But the real issue here, I suspect, is an emotional one.
- It feels deceitful and opportunistic to apply for a college you are not keen to attend, just to have options. That's probably because applying for it somewhat implicates pretending that you do.
- It feels ungrateful and egoistic to ask for recommendation letters for some applications and then not accepting any of the offers they have helped you get.
Also, and maybe most importantly, there is a feeling of selling yourself short in applying for colleges “you don’t really want to end up in, but maybe would be better than nothing”. You are essentially leaving open the option for an act of desperation. And in preparing for despair, you are acknowledging that you would actually maybe act on it, which might feel undignified.
Hence I suspect this question has more dimensions than the purely strategic ones, which have already been handled well in the other answers. So I will give my considerations on these other dimensions:
If I am correct, I recommend you should come to terms now whether attending a college of second choice would indeed be an act of desperation for you and whether you would – in principle – be willing to act on desperation for your current goals or rather be willing to pursue a different path in your life. Only if you here realize that it would be an act of desperation that you actually are not willing to make, I recommend that you do not apply for these colleges.
If you feel just a bit unsure about your answers, you should also consider that you may be in a different emotional state when you are actually receiving offers. In this case, you should assume that you would want to have the option, that it will not seem like an act of desperation and, even if so, that you would be willing to do it anyway. Everything else may lead you to great regret.
Finally, you should realize that applying for colleges just to have options (as long as you don't go overboard) is an acceptable thing to do. You can be absolutely be forthright about your reasons for applying to them. If anyone else involved feels like these reasons are not good enough – well let them feel this way and let them act on it too. You will not feel deceitful or ungrateful. Worst thing that will happen is that you won’t get accepted to one of your second choice colleges, which is your alternative now anyhow.
So anyway: You write that you apply for three colleges you are unsure about. I think this is a very reasonable number for options. Hence I concur with everyone else in my recommendation, just with a minor reservation: Just apply to every one of the colleges you consider which to attend you would not consider an act of desperation you are not willing to make.
(Well, that’s basically what Orntt already said, just fleshed out.)
Come to think of it, my main advice would be that you don’t put off an inner confrontation you might face in the hope of avoiding it by being accepted to a first choice college. Confront yourself now.