I can't make a straight leg?

RedVelvetCurls

Hi guys, I'm about to start level 3 of Ripped in 30 and I'm having a blast. I love it. But I worry a little because I can't make my legs as straight as Jillian or her two helpers can. I know that Shelley is super flexible, as is Basheera, but even Jillian (who said she isn't very flexible) can make a straighter leg that I can.

Is this just the way my body is or is there something wrong with me? Does anyone else have this issue at all, and has it hindered your results?
I always push as hard as I can (having done 30DS thrice before this); I love FEELING a workout, but I just can't see myself getting the most benefit when I can't even straighten out my legs. And this isn't just while working out, it's all the time. :grumble: