I didn't jump the box

In September I joined the FitClub at work.  This is a group who meets up to 3 times a week to do a cross-fit routine.  I had been thinking about improving my running pace and everything I read told me I needed to add some cross training - apparently running 20+ miles per week isn't enough.
I have enjoyed this training for two reasons.
1.  It challenges me.  I would not do squats or lunges or kettle ball on my own - wouldn't know where to start.  And even if I did, I would probably not push myself.
2.  It is like working out together but alone.  The leader puts the warm-up and workout on a white board.  The group begins at the same time but we all work at our own pace.  So it is okay that it takes me longer to do the burpees because they are not waiting on me.  And no one is really counting.  You do what you can do but because you are in a group, you push yourself a bit too.
However - I wimped out yesterday.  One of the stations was the box.  It is about 18" high and you can do a step up OR you can jump.  I really did not think I could do the jump - so I didn't.  Truth be told - I had a bit of trouble doing the step up.  By the 4th round, I wanted to quit.  But now I wonder.  Could I have jumped the box?  I think maybe I could have.  Of course it is never too late.  There is a similar concrete slab at the trail where I will run this afternoon so maybe, just maybe, I will try to jump the box.  And next time it comes up at FitClub, I will push myself to try it again.