The first thing is to set your servo arms 90º to the links. If they are perfectly 90 and your linkages are the same length, then your swash will be level. If it's not level, then the linkages or the arms could be off, but you will have to find out what the issue is. And make sure you are in DIR mode, but you can use subtrim to perfectly adjust the setup. But you MUST be in DIR mode.