Gracie Brazilian jiu-jitsu Vol 2 – Advanced Arm Locks

I studied a video called “Gracie Brazilian jiu-jitsu Vol 2 – Advanced Arm Locks” by Renzo Gracie and Craig Kukuk. Renzo Gracie is a Black Belt in Gracie Jiu-Jitsu and is one of the greatest in the history of the sport. Craig Kukuk is the first American to receive an authentic Black Belt in Gracie Jiu-Jitsu. After, I studied it I tried out the techniques from the tape on a guy named David who has been training BJJ for three years. The first move on the tape is double arm lock from guard. You have your partner in your guard and he places his hands on your chest. You walk your legs up your partner’s back until they are over his shoulders and lock your feet together. You lock both his arms with both your hands. One hand locks your training partner’s hands and your other hand locks his elbows. Then you just pull your pelvis up.
I tried this technique, but I could not get it to work. Why? Well, one, it is hard to lock your partner’s shoulders. David would place his elbows in to my thighs. So, I grabbed one of his elbows with one hand and his wrist with my other hand: two hands on one. I tried locking his arms as I walked up his shoulders but it did not work. I tried what the videos says, and turn my hips but then David some how got to mount. It happened really fast.
I watched a youtube video on how to escape from full mount (I can not find it now). It said to bridge up until your partner has both his hands on the mat. Then, lock your arms around your partners’ hips to whole him there. Then trap a leg, and look for an arm and then trap it. Then roll over on side of the trip arm and leg. Well, I try that when David had mount but he locked his arm together and I could do anything.
Can anyone tell me what I should have done?
The other techniques on the video I did not get a chance to use. So I will comment on them later.