your left and right will always vary depending on which is your dominant hand. definitely focus on barbell exercises (for even weight distribution) and make sure with free weights that you dont keep maxing out your right arm while fizzling out with your left. i'd measure and double check the difference isn't just in your head, and maybe modify your workouts for some extra tricep pulldowns or wtv with whichever arm is lacking.
mine is pretty uneven, but i think its normal
