You're welcome =)

It worked ! thank you HAL 9000

Yes, that unused block is the second block you come across as you move to the left. You won't need to use it. After pushing this second block up, move forward and push the bottom-left block left once, then go back and go around the one above it. Like this: u-l-l-u-l-l-d-l-r-u-u-l-d-l-dddddd.... Then two different ordering is possible, I think one will be 135 steps and the other will be 133 steps.

That cyan block unused is the second you encounter from the start pushed up? I don't get how you move the 2 cyan blocks on the left even backtracking your steps... thank you