you haven't ruined your life; not even close. If I could do it all over again, I'd keep the "practical/backup" major and minor in music. And take more than just the minimum required courses for the music minor - if you think you want to leave the door open for getting a masters in music, look at what those programs require and take those courses. (The schools I considered for a masters required 2 semesters of music history, 4 semesters of theory, ear training and piano/keyboard skills, and 2 semesters each of French, Italian, and German.) You'll also want to take advantage of whatever performing opportunities are open to music minors. Every school is different, but where I did my bachelors in music, opera workshop and the collegium (early music performance) were open to all students who successfully auditioned, not just music majors. Ask and find out what performing opportunities and ensembles are open to music minors at your school.