The best thing I ever did for myself during the recruitment process was just assume it's in the bag. If not with this airline then another. I then relaxed and forgot about things until I got those nailbiting emails...
It helped enormously because no matter what happened everything was just fine and proceeding the way it should. I could get on with my life until such time as I was told it was going to change..
Don't doubt yourself, getting the progression email is confirmation enough that based on what they've seen, you've got the right stuff. What's the worst that could happen? You'd be confident that you're going to get a job and then they say no. I promise you, it's not any easier to take if you are doubting yourself along the way.