What is everything i need to know about child support?

I am separated(still legally married) and i am giving my ex money for my child but i want to do it legally in case she turns around and says i never gave her any money. I was calculating how much they would make me pay(based on a texas website)and it’s a crazy amount, my child would not need that much money. It said i would need to give $640!!!! What can i do to better my situation?

Also, is there a difference between me putting myself in child support vs her putting me on it? Will it look bad on me if she does it?