I noticed the gap between the fender and door is wider on the passenger's side than the driver's side. Is this a factory defect? I sometimes am paranoid that I opened the passenger door too wide and messed up a hinge or something. The door closes fine with no creaks or squeaks or squeals. Is it possible I opened the door too wide and slightly tweaked a hinge? I've noticed some early '15 mustangs had body panel defects, not sure that's my issue.

Relax I doubt you tweaked the hinge by just opening & closing the door. Uneven panel gaps are usually due to an inattentive worker at the Ford assembly plant. Seems the S550's are especially troublesome around the rear deck lid/rear fenders. The gap on your door can be fixed rather easily though if it is bothering you. You can try doing it yourself, but I would suggest using a body shop since they have all the proper tools and shims (if required). The doors on a car, while bolted to the hinges, are actually designed so their position can be adjusted before all the bolts are fully tightened. As long as the front edge of the door isn't so close to the rear edge of the fender you shouldn't have to worry about any interference between the two.

U.M.

Had the same issue with the hood/fender gaps when I bought my mustang...dealer adjusted the hood for free. They told me that some of the body panel gaps coming from the factory can be less than perfect but are easily fixed.