iCloud somehow linked to sister's iPad, not my iPhone

I just bought a new macbook pro for college today and decided to try iCloud so that I could sync all of my data into one place. However after adding my apple ID info and finishing the process, all of my sister's photos and data showed up instead. The odd part is that even when I tried out the "Find My iPhone feature, THAT did find MY iPhone. Did our accounts get overlapped somehow or something? Any help would be great, thank you!