What crosstrack should I have during a holding pattern?
If you follow the holding guidelines you will never leave the protected area. This includes performing an appropriate entry, applying correct wind correction, and flying the correct leg length.

ATC expects you to slow to holding speed no later than 3 mins before arriving at the holding fix for planning purposes, and generally doesn't expect you to use the entire protected area. However, the entire area is protected, so you could use it if you wish.