Shoulder imbalance can happen because of spine problem and can happen because of Scoliosis so any scoliosis in the thoracic spine can lead to a shoulder imbalance so first thing that needs to be seen is any problem with the spine per se other important causes can be wasting of muscles around the shoulder joint and can lead to a shoulder imbalance which can happen because of some nerve rest in the neck can lead to dinner version of the muscles around the shoulder and lead to weakness and wasting out the muscles around the shoulder so it needs evaluation maybe x-rays and then any opinion can be given

Hello dear Thanks for reaching out. I don't see a shoulder bigger or smaller, however i do see a higher right and a lower left shoulder. Now since you don't have any complaints, there is no urgency as such. But if you have been getting repeated neck pains i would want to see the same thing from behind since scapular dyskinesia is a known problem in young individuals and can cause neck and shoulder pains in future too if not addressed properly. Just to clarify such kind of thing doesn't occur by a day or two of gymming. You must have had it even earlier, probably you just noticed recently Regards Dr Vipin Gupta

A shoulder n spine examination is needed . However slight asymmetry is a common occurrence .

This is a common problem, when you are not doing the exercise with proper technique. As you have no pain, nothing to worry. Just ask your trainer to work on your weak part.

Hello.. The right shoulder doesn't appear to be smaller but there seems to be slight bony prominence of bones on right side.. may be because of shadow on left side. As you dont have any pain, there is less likely to be some cause related to workout..  

U need thorough shoulder examination, consult an orthopedic surgeon.