As long as you show up to the "big" events (concerts, etc.), that actually feature the band, I don't think it matters if you miss the lesser events like this pep rally.
And no, you aren't a bad father. My parents used to always miss the same track meet every year (on purpose) because it was poorly organized, took twice as long as it should have, and they simply didn't want to sit through it. I didn't care - what was important was that I knew they supported me and they each made an effort to attend at least a few events each season.