Deadlift form + problem

[ssharon95]

Start At 00:35
https://www.youtube.com/watch?v=wBzfEwccAkM

My set-up looks good but when i start the lift i (idk why) i just raise my ass , that driving me crazy!! , there is a tiny improvente from the previous video but still the technique dont look "great" .
Even with a lightweight (When im trying very hard to stay low) im raising my ass first..
I didnt raise weight for 2 workout because i tryed to fixed my technique.(SS)
I forgot to mantion that at the set-up (low) i feel a hard strech in the quads, if that mean anything.

Is someone had that problem or something similar befor?
Any solutions, tips or something will be welcome! Thanks.!

My previous video
00:20
https://www.youtube.com/watch?v=EEp-fP3CmeU