I would just ask her, the cheerleader, to the dance or even just to hang out. I don't think you need to tell her you like her, I mean, when you ask someone out, it's assumed that you do like her! And then just see what she's like on a date or whatever. As for the other girl, there could be several reasons for the jealousy as tiinkerbelle pointed out.
Now, as for that situation today, I would just make sure everyone knew you didn't say she was ugly. Other than that, ignore it... notes can be a good sign, trust me, I would know!