about the head-lead dolphin

hi, i'm a new for learning butterfly by the movie from youtube:
https://www.youtube.com/watch?v=twGoqn1_wWM&t=697s

here are some problem:
1. when i'm pulsing my chest, just can't help kicking my leg, is this normal?
2. maybe my ankle doesn't have flexibility, i bought fin and expected some progress, but it doesn't work for me, i can't move forward without fin, even worse, i move back when i tried do the head-lead dolphin. could i ask for some suggestion from you? or just practice more?