All that hair and you're using yellow rollers?!
You should definitely go up some sizes. At least purple, but black and grey will probably be your best bet, especially if you are going for a straighter style.
And I think you should try four sections, or a ponytail set...they provide the same results as the mohawk, and in my opinion, they are easier to manage, because the parting is less complicated.
Lastly, maybe you could practice anchoring on dry hair, until you find the best way to place the clips? I find that my rollers stay in best when I place the clip as far towards the front of the roller as possible, while making sure that the roller is not being clipped to a piece of hair in front of it. I hope that made sense...it's kind of hard to explain what I mean.