Idk if I'm right or not, but I like to end my body part with single arm excersizes.
End chest day wouth flys or somethin with dumbells. Also, pay attention to your form. You could be lifting asymmetrically. You could be doin the same amount of reps, but youre doin the reps different. Dont continue with both sides if one side is failing..
Personally, I wouldnt train one side alone. I would just try and make sure to always train them evenly. Eventually they should even out.