If your sidebar is turned on and you don't see in on your listings, it could be due to either:
Reason 1: Mobile Display
If you're viewing your listing design on mobile, some templates will hide the sidebar, or put it at the bottom.
Reason 2: Store Listing Frame
If you have an eBay Store subscription, eBay's default left sidebar may be forcing your design to hide your sidebar (not enough space).
To disable eBay's sidebar:
under Store Header Features,
choose either Store Header Only
After clicking Apply at the bottom of your screen, eBay's sidebar will be removed and your 3Dsellers sidebar will be displayed.