I get by with a little help from my friends...

So I have cast on for Sizzle in the size S, using Bendigo Mills Harmony (cotton / wool / lycra). I went up a needle size to get gauge but as I'm halfway through the back, I've a strong feeling that it is going to be too large and bagmatic. I'm not convinced I have the mettle to knit it only to try it on and find that it's far too big. Can someone give me some idea of their body size and whether I should rip out and cast on the x-small?