Yeah don't say that it sounds creepy. If you are really good looking yourself and the talk of all the Sixth Form girls then you might get away with it but if you're just average and don't have loads of female admirers then saying that will immediately put you in a box in her mind which is [unwanted admirer: avoid all contact].
You need to find some form of relevant conversation or find some kind of social occasion where you can just start making conversation and it doesn't look weird. When you go up to make conversation with someone you fancy its got to be natural and easy flowing conversation, if you just turn up and start talking at her there will be awkward silences and the interaction does more harm than good.
I suggest playing the long game and waiting till you get an appropriate opportunity. A few months back a really attractive girl started where I work, she works on the same floor as me but not the same section directly so I didn't really have an "in" to speak to her and it would have felt weird to just turn up and start chatting. Then one time it was someone's leaving do, people tend to leave at different times depending on when they've finished whatever they are doing, and as I was nearly finishing I saw she was packing up too so I thought I'd take the off chance that she might be going to it and I went up and asked her, she was, so we walked down together, got drinks at the bar together and sat together chatting for ages: the interaction felt kind of normal and social and was easy. Now that ice has been broken we always chat if we bump in to each other in the corridor etc. Not sure if I'm going to necessarily pursue it by asking her out but I feel like the door is open now, I can email her and ask if she fancies going down for lunch together etc.