What are you doing at the gym? I'd say don't expect too much in three weeks - even if you only lose 6lbs over the course of the three weeks for example, you're probably gonna be better off writing down your measurements. You want to look less bulky, right? So do some toning exercises, maybe get an abs workout DVD or go to a Zumba class, do some spinning, butt clenches, stomach clenches, stuff like that...
I wouldn't predict big losses in terms of weight but it's definitely worth taking your measurements now and then before you go away, doing them every day won't get you anywhere and will probably really frustrate you.
Sorry for the total unhelpfulness of this post but I really didn't want to read and dash, especially as you've just joined the FlabFighters challenge!
Ali xxx