How to make an IMG fill a thread?

[53]

Hello, I created a thread design for a product im trying to sell. its 3840x8000, I upload it to imgbb and copy the bb code to post it to the forum. However it only pastes down the middle and doesnt "fill" the thread.

How would I go about making this image take the entirety of the thread post?

[5.505]

Code:

[img][/img]

[Object: Error]