Please try not to be too hard on yourself. I am now able to travel, as you saw on the other thread, but I have to plan it and I still have times when I unexpectedly just can't manage to pee, even at home if I'm under a lot of stress. I've been doing this long enough now though to know that just because I'm not able to pee on one occasion doesn't mean that I won't on the next. The lack of logic drives me potty but that's the way it is for me.
I still limit fluids when I'm travelling too. Long ago I tried doing the opposite and drinking loads in the hope that I would simply have to pee but oh my goodness that was distastrous for me, although maybe it works for other people. I always take a cysitis treatment with me in case I take it a bit too far and give myself cystitis - that used to happen quite a bit.
I'm an extremely keen traveller and it would grieve me enormously not to be able to travel. You are doing really well to tackle a flight and to use airport toilets which can be daunting. I've had some difficult moments in both but it is possible to find your best ways of dealing with them. Please try not to see this as failure but as one of the twists and turns of living with paruresis.