How to get child custody modification

Right now, me and my ex wife have joint custody of our 3 year old son with her being primary. She has him 60% and I have him 40%. I also pay 500 in child support, even though Im suppose to have him almost half the time. Well she always claims that she is busy with work and school or studying and she lets me have him on a lot of her days. I have him all of my time and a lot of her time too. I added up the days so far this year (6 months) and I have had him way more than she has. Right now I have him 60% and she has him 40%. I have kept a calendar where I recorded all the days she gave up her time so I have proof. I don’t think it’s right that I have him way more than her and I’m still having to pay her child support. I also don’t think it’s right that I have him so much more, yet she gets to make all the final decisions about him because she has primary. Can I take her back to court and get a custody modification and a child support modification using the proof that I have?