Newsround Lite caught up with the girls to find about their new lives as pop stars and their hopes for Christmas number one.
What's the latest in the fight for number one?
Nicola: We're ahead by a couple of hundred so we need the girls to keep behind us otherwise the boys might catch up. There's a few days left so keep buying it.
Kimberley: We're never safe, not until Sunday!
How often do the numbers change and do you trust the numbers that you're hearing now?
Kimberley: Obviously the first couple of days it does count because lots of fans will go out and buy it in the first couple of days but anything can happen.
Every day is different and we can't be complacent and sit back - we need everyone to buy it. Buy five copies each - that'll be enough!
How many copies have you bought?
Sarah: None, it's against the law for us to buy anything.
When this whole thing started out the boys were the favourite - why do you think you're now winning the race for number one?
Cheryl:There's no one out there at the moment that's a strong five piece girl group and there are lots of boy bands.
We're bringing something new and fresh and a brilliant track whereas they are just bringing out the same old thing.
Sarah: It's the battle of the sexes. We're going to prove them wrong.
It's a great song - what did you think when you first heard it?
Nicola: We loved it.
Cheryl: We heard it and we called the record company and said we really love Sound of the Underground and we really want to record Stay. They said that we could and here we are.
The boys are talking about dirty tricks, about you coming out with slogans to sell things and making some suggestions about session singers on your CD. How do you feel when the boys say things like that?
Kimberley: It makes them look a bit desperate - it's silly.
Sarah: We've put a lot of hard work into this and for them to say that is a bit insulting. We're having a bit of fun with it.
How important is it to you to get to number one?
Nadine: It's not really that important to be honest - we've just enjoyed everything we've been doing.
Cheryl: It would be amazing to be number one but we just want a long career as a group.
What's Louis like to work with?
Nicola: He's lovely - He thinks he's one of us sometimes!
What's the harshest thing he's ever said to you?
Cheryl: 'Cheryl don't ever wear your hair like that again - it's awful!'
Nadine: 'Nadine those trousers make you look like a grandma'
Cheryl: He's very straight down the line and honest.
What do you think of the Cheeky Girls - they might get Christmas number three?
Nadine: Well done to them. They auditioned for the competition and they've done so well from it - go on!
How does the reality of being a pop star compare with what you thought it'd be like?
Sarah: It's harder work.
Cheryl: You can't really have expectations in this business - you've just got to take each day and see what happens.
The early mornings and everything - it's hard work and it's not all glamour but it's worth every single minute.
What's your message for the boys?
Good luck boys we hope you do very well. May the best song win!