College choir, singing secular and catholic songs, although I don't see how that is relevant.

To add further context, I am not specifically required to attend. I may legitimately opt-out, however, I don't know what will happen if I don't come to all competitions on Sundays.

This is the first such occurrence in 9 months. I would say it could happen twice a year at the most.

It is permitted to miss Mass if travelling and, per a sermon I saw from Bishop Sanborn (someone posted it here once), you are dispensed from the obligation if there's no (acceptable Catholic) Mass within an hour of your location, or if there are other logistical issues making it burdensome to assist.  There need not be some grave reason for the travel ... could simply be that you want to go on a vacation, or for any legitimate activity.  Choir competition would be perfectly legitimate.  Now, if someone were travelling to engage in something sinful or illicit or otherwise illegitimate, then the person would also be guilty of missing Mass.

There is, however, no backup obligation to do anything else to make up for it (viewing online Mass, reading the Missal, etc.).  While those are highly recommended, either you can assist at Mass or you can't, and there's no law that requires some specific kind of backup activity ... although there should be some reasonable attempt to conform to the general divine law of keeping the day holy ... as much a possible.

There would be no reason for you to be troubled by it.

Now, depending on your conscience, even if there's no Tridentine Mass, there may in fact be Eastern Rite Masses in the area.  I consider them to be valid and, apart from, say, the Maronite Rite, acceptable for a Catholic to assist at.  When I've travelled, if there was an Eastern Rite Liturgy within range, I would consider myself obligated to attend if possible (i.e. if not prevented by other considerations, such as logistics, etc.)