Cant get all the way up in MN/PE2

I find myself not able to sit up all the way with the legs out like the MN/PE2 demo video, i stretch my hip flexors almost everyday and i've been doing some exercises for it, not sure what the name of it, but its pretty much sitting on the ground legs open straight out, and you lift it off the ground keeping legs straight, i feel the cramp directly on the hip flexors. I do that almost everyday too

 

So my question is, should i continue doing those, or are there some other stretches/exercises i can do to be able to raise my leg more towards my chest in MN/PE2

https://www.youtube.com/watch?v=n78PS4zq3D8

 

 

 

A stretch that helps me out a great deal is the seated hamstring stretch. Laying flat on back, place a long cloth/strap under your foot and pull foot up in the air, holding on to cloth/strap. try to get past 90 degree angle.

I found that my hamstrings had to be flexible enough to stretch, and the hip flexors strong enough to lift your legs up.  

 

Stretching the hip flexors might be good, but it won't get you more range in a straddle like that.  (Great for your splits though.)  You need to stretch the ham strings AND strengthen the hip flexors. 
 

The above stretch is good.  There are lots more.

 

If you want to work the hip flexors more, try floor slide mountain climbers.  Those helped me.