Am I a horrible step mom/wife??

Charlotte
My husband and I share a love of fitness and running. Our first official "date" was actually running a half marathon together. We we married exactly one year later and ran the same race the morning after our wedding in cute bride and groom outfits. 
Our first year anniversary is coming up and naturally I went ahead and registered us to run our race. I wanted it to kinda be our special thing. 
Well we just found out that my step daughter's FIFTH GRADE promotion is the day before our anniversary. She lives over eight hours away ...we were originally planning on getting step kids for the summer a few days after our anniversary. 
Now my husband wants to travel all the way there for her graduation and get his kids early for the summer. This will mean that we will miss our race and spend our first wedding anniversary in a hotel room with my step kids. 
I get that it's not fair that he would have to miss out on life events because we live so far away, but it's just 5th grade and she has already made it clear that it's not a big deal to her. 
I don't want to make him feel like he has to chose between me and his kids. But it's our first wedding anniversary. 
Any suggestions on how to react? Or compromise? I've already looked into running a half marathon in their town but there aren't any that weekend. There isn't even a 5k! 
Am I a terrible person for being upset about this??