Sum What-if parameter value with column value with IF function

I'm trying to create a measure that adds a what-if parameter ('PA Cost Adjustment'[PA Cost Adjustment Value])

to a column ('Forecast'[Budget]) only when another column is a certain value ('Forecast'[Sector]="B").

In Excel, I would use a formula like this:

=IF([@Sector]="B",[@Budget]+PA Cost Adjustment Value,[@Budget])

where PA Cost Adjustment Value is a named range.

I tried creating a measure with an IF statement

Scenario Budget = IF(Contains(Forecast|Forecast[Sector]|"B")|SUM(Forecast[Budget])+'PA Cost Adjustment'[PA Cost Adjustment Value]|SUM(Forecast[Budget]))

which will calculate the correct value for a single year, but if you sum up all years, the what-if parameter is only added once instead of 4 times.

Here's a sample of the table ('Forecast')

I'm sure I'm making a rookie mistake but I despite hours of googling solutions and watching videos, I can't figure it out! Thanks in advance for your help!