I would ask the dealership to check the alignment again. Whether you tell them what you already know is up to you.
If the rear wheel is out of alignment, that should be covered by your bumper-to-bumper warranty. Plus this -
In addition to the warranties listed above, every new Mitsubishi also comes with Restraint System coverage for seat belts and airbags of 5 years or 60,000 miles under the New Vehicle Limited Warranty, along with 12 months/12,000 miles coverage for adjustments; if required as a result of a manufacturing defect.
Dealing with this issue early on is probably best!