Darn, how tall are you? 55kg is almost where I started. No I cannot suggest that then. Just keep bulking
Lateral Raises are one of the best exercises to make your shoulders broader, but keep your expectations realistic, natural bodybuilders have to put a lot of effort/volume/time into their side delts/lateral delts to get them to grow where as an enhanced person could just do compounds and get the same response. Do some lateral raises, keep the weight low, it's more focused on form and volume than weight. 8-12 reps is what I follow.
As for the right/left arm dilemma, the only reason it would look leaner is if it had more muscle mass, bodyfat spreads out across the body (except them damn calves xD) I see it a lot with 'skinnyfat' people, they are at about 13% bf but when they start bulking they actually look leaner because their muscles developing (noob gains). I am right dominant and my right arm is bigger than my left, all I can really do is a few more reps for the left arm.
Were you sedentary for the last few years? If I may use a big word