done
That it adds more columns is expected and unlikely to chance, as Asana uses all columns in the background, and an export is giving you the raw data.
If upon closer inspection there is actually a mismatch between the information in the project and the information in the export I would advise to contact support (Head’s up, they are quite busy so it might take some time before you get a reply)
If you’d want to filter out the columns you don’t use you can use Power Query. This allows you for instance to set up an Excel file that whatches a folder, and upon refresh data collects the current .csv file data, and removes, filters, and/or pivots the data in the way you specify.
I can help you set this up if you want. If you do send me a DM.