Are you feeling very wiped out with the extra exercises? If so have you tried increasing your carbs a little? It's perfectly fine to do more exercises - I would break lower and upper body into a 3 day split however. Instead of working upper then lower in one workout each you would be doing specific muscle groups with more exercises per group - triceps and chest one day, biceps, shoulders and abs another day, etc.

This is something I will be doing once challenge 2 is finished and I've taken some time off. I do think that following the exercise program as it is written for the first challenge is a good idea, though. You can't decide if it works for you or not (as written) unless you complete it, after all.

Nat