First of all…………………….AAAWWWWWWWWWW, HOW CUTE!!!!!!!!!!!!!!!!!!!!
You’re going to have to be really patient. Pet stores do ABSOLUTELY nothing about making a rabbit a human-friendly pet. They don’t spend time with them or socialize them, and they don’t usually use litter boxes at all. Your bunny has spent its entire little life thinking it’s okay to crap anywhere it wants, and you’ll have to be patient, and hang in there. My pet store bunny is only NOW using a litterbox on a regular basis, and he’s seven months old! We neutered him over a month ago, and it helped a lot.
Some helpful hints–your bunny will like a certain type of litter. Once you find out which one he likes most, and you’ll know because he uses the litter box more, DON’T change the brand. My rabbits will only use one kind, and God help me if I buy something else!
Make it easy for him! Hang his food, if possible and his water over the box in the cage, so he has to sit in it to eat and drink. One of my bunnies constantly poos while he’s eating, so this got him used to the box.
Keep it clean! Scoop every day, or even twice a day, if your bunny is a poo factory….. Leave just a few behind, so he can smell them there.
If you let him out of the cage, give him lots of boxes to choose from, and keep them all clean.
Hope this helps.