To be honest,, I completely understand where you are coming from. Insecurities suck, honestly, they do -- as I'm sure you're aware by now, right? x3 However, with all that in mind...
Brains, especially teenaged ones, are renowned for being massive liars. It thinks it's helping by telling you all these people are being cruel behind your back, but I can guarantee you, they aren't! This might sound a bit mean, but: no one cares enough to worry about someone's skin health. No one has the time in their day to gossip about others' acne, I promise you that there are dozens more teenagers with spots all over in your school than your brain lets you see.
And about the whole 'ugly' thing; you need to spin your thinking around. I heavily doubt you are ugly but, hey, even if you are -- what does that matter? Your looks don't dictate the way you behave, or the way you act, or the people you surround yourself by. Hell, I am not the most attractive lass, but I find myself comfortable in that fact -- I'm ugly, but that's fine!! It doesn't matter, I promise.
High school is hellish, but you'll be fine. You'll get through it. Keep pushing! :-)