Shortcuts Alt + S to zoom clip?

Hi, I am trying to learn some way to zooming. Right now i try to zoom the clip to fit the screen.

I am trying with Alt + S, it work but i need to press 2x Alt + S to zoom it perfectly to window. Is it normal ?

Just try to select a clip and press Alt + S and another Alt + S and it will fit on screen. If i press only 1 time the clip up and down is not exact in screen.

Am i using the right shortcuts ? It’s not a big problem i am curious. Tank you