Accepting and declining job offers

I applied for a small office job that doesn’t pay well and isn’t related to my college degree, but I applied anyway because I figured why not; it’s better than nothing since I currently don’t work. But I also applied for a “big girl” corporate job that is related to my degree and pays pretty well, so it’s obviously the better choice. But I’m pretty confident the first job will call me first. I don’t want to turn it down because what if the second job doesn’t call me and then I just screwed myself over? But I also don’t want to commit to the first job and then cancel on them if the second job calls me. How do I go about situations like these? Neither job has called me yet, but I just want to be prepared in case this happens. Thanks ladies for your help!