The gate itself is 29" and the screws on the side expand out about 5" so, the gate alone goes from 29" to 34".
It comes with a 6" extension and a 12" extension that can expand the gate to 52".
So if you need to go to 55" I recommend getting 1 additional 12" extension.
They don't recommend using more than 2 extensions. So use the included 12" extension and the additional one.
This should expand the gate to 53" - 58" which should be perfect.
You don't need to screw the cups into the wall unless you use this at the top of stairs. I don't use them myself and it's been perfectly stable.