So now my 17 year old cousin has a grade 2 heart murmur, leftward axis, and incomplete right bundle branch block. What can all this mean? I'm scared!

My best guess. Heart murmur, left axis deviation of the frontal plane qrs axis, and an rsr' in v1 (irbb) makes pediatric cardiologists suspicious of an osmium primum atrial septal defect. Typically, this presents in the first few months or years of life, but it can present in adulthood. To sort this out, your cousin needs an echocardiogram.