Hi Kayleigh,
well done for starting and a big welcome to the forum. I'm also on slim fast and I would definitely recommend drinking lots of water or squash, it really helps with the hunger.
im actually allowing myself 1600 calories a day, because 1200 for my size is way too low, so that means I can have 800 cal dinner, or an extra snack if I want it.
good luck with your weigh in, I'll be checking back to read up on your progress xxxx