I'm in the same boat bro. When I'm not on cycle both arms are pretty even, but when on cycle, my right arm greatly surpasses my left. I'm 6 weeks in on a cycle and my right arm is 3/4 inch bigger and it's noticable

What I have to do is add an extra 1-2 sets on my left arm on individual lifts and take away a set or 2 on my right for a fiew weeks, and usually I can get it to catch up...
Hope this helps bro