I'm 4'11 and 84 lbs and have been doing the 30 day squat challenge. I'm on day 25 and I noticed that the right side of my butt looks better than the left. It's rounder and more lifted. I was just wondering how I could balance them out.
That's pretty normal. Everyone tends to favor one side or the other -- usually your dominant side will be stronger. One side may always be slightly more toned than the other, but you can make the difference much less noticeable by doing alternating unilateral movements such as weighted lunges, step ups, pistols, split squats, etc.
An interesting solution for you might be to the following workout every 2nd day for 2 weeks.
Do some dynamic stretches.
Then only on your right side do a static glute stretch, this is so that you weaken the muscle on the right side a little, but please take extreme care not to over stretch as that can cause injury during the workout.
Now do a single leg squat on your right leg without any weights and on your left leg add 5LB in each hand and do the same.
You can incorporate this in any workout you are doing if you feel it will help.
Another option to look at is to do yoga, I have seen a lot of results in that area on myself with yoga.