So I just accidentally used a white scroll on throw away scrolling. I'm not the first or last to do so. While using legendary spirit, I realized it mid scroll and tried to click off the box for using the white scroll. Though the box became unchecked, I still used the white scroll. I suggest that if you click the box in time, you can unselect the white scroll and not use it. inb4 git good and pay attention, I'm an inattentive idiot.
You can't cancel it "mid scroll" because there is no "mid scroll" step. The scrolling happens as soon as you drop the scroll on the item. The animation afterwards is just an animation but the scrolling has already been done. You can verify it yourself by using a scroll on an item in the legendary spirit window, then switching to equip tab in your inventory and hovering over the item, you will see the result of the scrolling before the legendary spirit animation finishes.
This. I keep my ws in storage and only take them out to use them. If you never hold them in your inv you can't accidentally burn them.