Yeah, I have had the same experience. I asked the trainers and two different ones simply suggested that I do more reps/sets with the smaller/weaker side.

I think all of us are asymetrical...some are just more noticeable than others..and if you want to correct it apparently it's pretty simple.

Frankly, I didn't work that hard to up the reps and my left thigh (quad) and upper arm (bicep/tricep) are still smaller than the right.

Let me know if you have success?