Not Ready for 30 Day Shred

A group of my friends started Jillian Michael's 30 day Shred a couple of weeks ago. I did three days and it was awful. The strength training and the crunches I can do without a problem but the cardio is really tough for me. I feel like a failure even saying that out loud especially when I read that it is targeted to beginners. I can walk 2 miles at 4mph without getting winded but 5 jumping jacks and I feel like I’m going to die.

So is there a better one out there for true beginners? Should I keep it up and just walk in place? Any suggestions??