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.
Please check and contrast this information, because I am no expert at all, but just an amateur that has recently started reading and learning. Simply read this and judge by yourself:
Probably, the best thing you can do is an asymmetric butt exercise like a Dumbbell Stiff Leg Deadlift, but don't work only on one side. The good thing of an asymmetric exercise is that you are ensuring that each side of your body works independently, so that the weaker side is forced to develop at the same rate than the stronger one. The classical example is the Bench Press: some people unconsciously push much more with one side, and the weaker side works only to maintain the bar horizontal during the lift. When they notice an asymmetric development in the mirror, they switch to Dumbbell Bench Press for a while, so that each side is forced to work independently. I guess it is the same with your butt. So, do that Stiff Leg Deadlifts in equal numbers for each leg.
Second, many people have a leg slightly larger than the other (and thus an asymmetric hip position) and never notice it in their entire life, because it is completely irrelevant, but for some minor aesthetic effects that mostly go unnoticed, and cause a mild and unimportant scoliosis. That may or may not be your case.
Third, it might be a good idea to keep on doing squats, but with the goal of strengthening and bulking up your butt. That can be easily done at home by means of Goblet Squat with a sandbag or similar. When you do some sets of, say, ten reps, add a little bit of sand to the bag in the next workout (just go adding small increments at constant reps, forget about the going-to-failure and no-pain-no-gain bullshit that has got many of us injured). Learn carefully how to do the goblet squats with proper form before starting, no matter how many bodyweight squats you are now used to. When there is additional weight, proper form matters much more.
Another good exercise are the lunges.
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.