X-ray: mild left convex cervicothoracic scoliosis w/reversal of upper cervical lordosis. minimal subluxation is evident at c3-4 level. should i worry?

No: However you may want to see if you have a short leg. Tha t ca cause the neck curve, also be attentive to your posture.

Scoliosis : Mild scoliosis, min subluxation may not mean anything depending on actual numbers. Many people can have very small spinal asymmetry. Reversal of lordosis may be a sign of spasm. Either way i think you are getting the idea that one would need to see the actual films. An even more important question is why you got the films in the first place: your symptoms and your neuro exam.