It really depends on the girl. Some girls use sweet as a part of normal everyday use - in which case you may be in the friend zone. (It's kinda hard to tell just from what you've said.) On the other hand, I only tell someone that they're sweet if I like them.
As to the other part of your question, if you're in the friend zone, you can get out of the friend zone. The best way is to subtly start to flirt. I say subtle because if she's only looking for friendship you don't want to scare her away before she can tell if she has those kind of feelings for you. Just a word of warning though, if you are in the friend zone, this is going to take patience on your part. For example, if I start to like a guy that I'm friends with it always takes me a lot longer to move to the next step. I think it's because I really have to put thought into whether or not it is worth it to jeopardize the friendship.
Hope this helps.