I had one alcoholic drink about 4 hours after taking azithromycin. will it affect the treatment?

It is doubtful that consuming one alcoholic beverage four hours after taking azithromycin will have a major impact on the course of treatment. It is not known that alcohol and the antibiotic azithromycin will interact negatively. Alcohol use, however, may lower the effectiveness of your immune system and raise the possibility of negative side effects like nausea, vertigo, and liver strain. Even if one drink is usually harmless, it's advisable to avoid alcohol while taking antibiotics in order to promote a full recovery and reduce any possible negative effects. Always heed the advice of your health care practitioner, and for detailed instructions, see the drug guidelines.

You will be fine. The azithromycin will be unaffected.
However it is always a good idea to avoid alcohol while being treated with antibiotics for any type of infection. This is so you can give your body the best chance possible to fight off the infection.
https://www.drugs.com/interactions-check.php?drug_list=300-0,1034-0