Hitler was ticked at what happened at Munich, he had been denied his chance to show off the Nazi military, which he was itching to do.....so he knew he had to make the demands on Poland so severe, that there was no way that the Allies were going to acquiesce next time.
Correct, he felt cheated. The generals did not want to go to war in 38. However long standing hatred for Poland among the military, even more so than Hitler, saw no opposition to the invasion of Poland in 39.