Miscommunications in the Work Environment

When I was in high school I worked at an animal hospital, where I was the youngest employee, and the only one still in high school. Because of this fact, I feel like the other people who worked there took advantage of their seniority over me and I was never able to get a day off because no on else would work.
On one specific occasion, after I had been working there for over 3 months, I told my boss that I had soccer championships coming up and would not know exactly which days I would need off. I guess I assumed that by telling her in advance that she would be more inclined to help me find someone to cover my shifts, if needed.
Then, the day came and I informed my boss almost a week in advance about the game. She, for some reason, put me on the schedule anyways to work that exact shift that was during my game. I asked everyone who works there if they could cover for me, and of course, no one would. I told my boss that I was not going to be able to make it, but she refused to help me find someone to work.
Even on the morning of the game I wasn't sure what I was going to do. I had already made a commitment to both my work and my team. I thought long and hard about it, and finally decided that I would be more beneficial to go to work. The reason I chose work was because only one other girl was working that day and there was no way she could have done everything by herself. It wasn't her fault no one else would work, and I didn't want her to suffer because of it. I decided that my team had plenty of substitutes and that this would give another one of the girls a chance to play, since I was a starter.
My team lost that game during finals. I quit my job the next week because they gave me no flexibility and I felt that I had been walked all over. To this day, I regret missing that game. Who knows if we would have won had I been there.
But at the same time, I think that I would probably make the same choice today, just because it wasn't fair to that one girl at work.
I don't know which decision was right. But I know that I handled the situation by weighing each option, then I made a choice based on my morals.
I would like to hope that this type of predicament won't happen again, but I know it will. And all I can do is follow my heart to make the right choice.