You say you have just joined though - maybe its not all a real gain, as your scales at home might be out of sync with the SW scales (so you might have been heavier than you thought to start with, before all the booze and fun)
Doesnt really help though I suppose - (its just i have a 3 week holiday coming up and I'm scared at what I could gain!!!)
Still, you are sure to have a great 1st week loss as to go from 3 weeks of drunken debauchery to the slimming world plan should show a really good result