How was the flight? I can imagine you had a lot of fears over that, but the major ones were probably dealing with people just to get on and off that thing.
I have a flight coming up in just under a week. I'm in the UK so I don't have a lot of insane rules in regards to visas and providing a ton of information. In some instances I can really just turn up and that's it. But even then, I have those same thoughts you had. That what if? question over every minor thing.
I think this is something that sort of dies down with experience though. The more you travel, the more you know what to expect and can easily prep.
Have fun! :^)
I can say that I have considerable flight experience because the Philippines is an archipelago, so I had no issues with getting on an airplane. But you're right; the anxiety is different when facing an immigration officer. Dealing with border controls in the three countries (Vietnam, Laos, and Thailand) is also nerve-wracking, even if they're mostly lenient with Southeast Asians.