The 20 msr is not like running in a straight line. When you get to one end you have to slow down, stop, turn around, then wait for the beep before taking off again. But then since the first stages are walking pace, I'm sure even without practice you'll get used to it pretty quick. Not to be overly sensitive, but running on the gym's hard floor sure isn't quite as comfortable as running on a nice, rubber-paved, knee-saving, competition-grade track with a nice breeze, superb scenery and plenty of fresh oxygen... LOL.
Really, to meet stage 6, the minimum for our age group, I think you can do that without being able to even run 2.4km. Just being able to keep a jogging pace for 8 minutes or so will get you to stage 6. But that's just asking for the undue attention from the course instructors.