You will succeed this time and when you sit on that plane seat you will have plenty of room in that seat.
I have not had to get an expander, but have had to suffer that awkward shuffle of the person sitting to me because my arms are taking up their armrest and space. I no longer have to try and make myself small. I still have 5st to lose, but losing almost 3 stones makes so much difference.
I wish you all the best on your journey.