I wouldn't expect too much from a 3 month old. They are so small they can't hold it long. I would use the kennel some and I will also suggest that you get a baby playpen or an xpen which is an animal pen you can get at any pet store. When you come in and he didn't go put him in the pen. Hopefully if you do this he will get the idea. I would take him out every hour until he start to respond some. My girl is 4 mos old and still makes a mistake now and then. I have had her since she was 8 weeks.
I hope this helps and hang in there.
