Yes, please change "-45" to "\-45" or @"-45" or " -45 "
For historical reasons, a leading minus character will be treated to mean the label is associated with a minor tick. (The tick will be slightly shorter.) To display the leading minus character, there are two methods:
(a) Escape with a leading backslash. In C# syntax, the backslash is also a special character and it needs to be escape by another backslash, so it becomes "\-45".
(b) Use a space character as the leading character like " -45 ". It is also good to also add a trialing space. This ensures the label will stay at the same position as it is center aligned at the same point. (The center of the label does not change even if the length changes.)