darnit. i just wrote a big long post and i lost it.
i think that low fluid, if they can't account for any leakage or loss any other way, can sometimes be an indicator that the baby isn't producing enough fluid, which in turn can signal some kind of problem with kidneys or bladder function. i don't know how common that is but i'm sure your doc is just being careful about it. low fluid can also increase the risk of club foot if left too long and cord prolapse during vaginal delivery.
i can imagine it must be pretty stressful to be told you are going in on friday with so little time to get used to the idea. i'm sure the doc just wants to be on the safe side and is keeping you and baby's best interests at heart. i feel for you. i am 36 weeks and a couple of days myself and it could happen to any of us i guess. come on here and vent to us anytime if you feel it will help you deal. i really hope everything goes well with the delivery. keep us posted on that and do your best not to stress, just try to go with the flow!!