Am I responsible for hitting a building when the Wheel stops are three feet to close to a building?

I was told by a storage place that I can back up to the Wheel stop and it's as simple as that so when I backed up to the Wheel stop, I tapped the building instead of the Wheel stop, I also explained it was my first time driving something that big and the instructions from the company was wrong. I also have three other people that witnessed the conversation.