Stuck at Sapientia, ocean boss?

[Bloempje]

So I'm at the chapter where a plane goes down and you encounter this ocean boss Sapientia. The first part is to destroy masks on his 4 legs, and then to press Y+B to go into finisher mode.

At that point you have 2 giant arms to control its direction. According to the game I have to steer and mash X, but every time I do, whenever the boss is halfway towards my sea creature monster, which I assume I am supposed to run into, the f*cker breaks free for some reason and I have to do this annoying cycle again.

What am I missing here? I've tried mashing X as fast as I can, I've tried pressing X only when steering, I've tried getting in a position where I don't see the controller prompt on screen anymore, nothing f*cking works and he breaks free at the exact same point everytime.

For whatever reason I seem to be stuck here, and I seem to be the only one having this problem since I don't see anyone mentioning this on Google. Would be a shame if I have to quit here.. *Also tried mouse and keyboard, but that makes even less sense.

[HellVein]

When you get to the boss strugling to break free you have to counter him by pressing a botton (a quicktime event)

[Bloempje]

Yeah, just got past him. Looked up some videos and apparantly you're supposed to get a Y+B prompt when he struggles free. Thanks anyway!