Add an extra column from excel source

Yes, I did go through all query steps. But still, I must have done something wrong.

let
 Source = Excel.Workbook(File.Contents("C:\Users\Jonas\Desktop\Privatbudget.xlsx"), null, true),
 #"Removed Other Columns" = Table.SelectColumns(Source,{"Name", "Data", "Item", "Kind", "Hidden"}),
 #"Power BI_Sheet" = #"Removed Other Columns"{[Item="Power BI",Kind="Sheet"]}[Data],
 #"Promoted Headers" = Table.PromoteHeaders(#"Power BI_Sheet", [PromoteAllScalars=true]),
 #"Changed Type" = Table.TransformColumnTypes(#"Promoted Headers",{{"Måned", type text}, {"Bruttoløn Jonas", Int64.Type}, {"Nettoløn Jonas", Int64.Type}, {"Overskydende skat/Særlige feriedage Jonas", Int64.Type}, {"Bruttoløn Signe", Int64.Type}, {"Nettoløn Signe", type number}, {"Overskydende skat/feriepenge Signe", Int64.Type}, {"Børnepenge", Int64.Type}, {"Mad", Int64.Type}, {"Opsparing - Oliver", Int64.Type}, {"Overført til lån", Int64.Type}, {"Netflix", Int64.Type}, {"HBO", Int64.Type}, {"Viaplay", Int64.Type}, {"Rengøring", Int64.Type}, {"Betalt bilregning inkl. Service", Int64.Type}, {"Yousee - overføres fra budget", Int64.Type}, {"El - overføres fra budget (1.050 kr)", Int64.Type}, {"Husleje", Int64.Type}, {"Angst-foreningen", type number}, {"A/C vand", Int64.Type}, {"Antenne", type number}, {"A conto varme", Int64.Type}, {"Gebyr for betaling af leje", Int64.Type}, {"Forsikringer", type number}, {"Licens", type number}, {"DJØF", Int64.Type}, {"TLF", Int64.Type}, {"MA", Int64.Type}, {"AKA", Int64.Type}, {"Jonas frisør", Int64.Type}, {"Vægtafgift", type number}, {"Ansvar + kasko", type number}, {"Bil diverse", Int64.Type}, {"FDM + vejhjælp", type number}, {"Yousee - trækkes fra lønkonto", Int64.Type}, {"EL - trækkes fra lønkonto", Int64.Type}})
in
 #"Changed Type

Step 6: Where I choose the colums I want to add, i just select them all. I can't see the colums, because its the sheets you choose under the tab "Choose colums". As said I only want to use the data from the tab "Power BI 2018" from my Excel source. And it is in this tab i made an extra colum.