It's quite normal...Everyone's embouchure is slightly different. Marcel Moyse played with his aperture off to the side, and did quite well. I also play slightly off-center. As long as the airstream connects with the edge of the embouchure hole at the proper angle, and you're able to control what you're doing to produce the sound you want, there should be no problem.

How far off center your aperture was could be part of the reason why you had so much trouble. If it's too far to the side, you begin to lose the fine control you need to play well. Slightly off center is not an issue in and of itself as long as you are still able to do what you want with your playing.

it has to do with the natural formation of your lips, if you have a tear-drop lip, as I do, you may tend to play off to the side and sound fine, if your lips are perfectly even, then you will tend to play in the center..no two flute embouchures are the same...