Pediatritian said 2 yr old ear infection was all cleared up. When we got home I opted out of giving him last dose of azithro. Is that ok?

Not a good strategy. In this case it is likely ok, if indeed on the follow up examination the ear looked clear. However, guidelines and recommendations for length of antibiotic therapy are designed to maximize cure and minimize creating resistant organisms. In the future completing the antibiotic course is the safest approach, unless of course the medications are creating side effects, in which case, call the doctor.
Probably. It is usually a better idea to finish all antibiotics prescribed for a course of treatment. Otherwise there is a higher chance or relapse or recurrence of infection. Missing the last dose or two often can be ok ..But certainly not always.. Nor is it recommended!