Also please see this FAQ for how to best debug your solution and ask for help.
Namely it would be nice if you put your code in a code block, and mentioned which programming language you are using.

Not a kata issue, your solution is wrong. It does not conform to followign requirement:

The number can be negative already, in which case no change is required.

The kata is badly written - post your code with a spoiler and I should be able to help. Your formula needs to do operations in the correct order.