Well I tried your save. It seems that it doesn't matter whether you fill the bar or not in QTE. You can move on the third phase of the battle no problem.
Well, the problem is I cant... I dont know what I am doing wrong, but I cant... I set the difficulty on Easy, and I turned off Difficult QTEs, but still I am unable to progress to the next phase in which should the whole bridge collapse...
I cutted first three tentacles, then there is the QTE for first time... I cant fill the QTE bar, so the tentacle knocks me off... then I am able to cut fourth tentacle, and there is the same scene again, I am on the tentacle and cant fill the bar... so down once again, and from now this scene is repeating again and again... I already tried it at least hundred times to fill the stupid QTE bar, but it is impossible for me, and without it I obviously cant move to the next phase of the battle... :(