Amniotic fluid smells different then urine... it smells sweeter, which is how you can tell. Or your MW/OB can test the Ph to be certain.
Also, the bag can re-seal... so if you really are are a ways out from really getting started you might just put your feet up and take some vitamin C to see if it will re-seal and buy you some time for labor to start, so that your provider doesn't start the clock on the 24-48 ROM rule... HTH!