Preemie and carseat?!

Mary

So my 4lb 10oz preemie is coming home hopefully next week after being in there for little over a month. They told us to bring her carseat in tomorrow to do a carseat test but we bought one before she was even born, it's the chicco keyfit carseat and it says it holds 4-30lbs, but when I looked at it the crotch buckle only has one slot so I cant put it back any further and I'm worried she wont fit. Has anyone used this carseat before or one like it??