I got into a massive fight with the guy I'm dating and I said some things that were probably out of line. I really want to apologise but I'm scared he'd regret it. I am genuinely sorry and all I want to do is tell him. It only happened yesterday but should I say sorry now or wait for a few more days?
Send him a text that says, "I said some things that I regret saying and I am afraid that I have hurt you too much. Please call me when you are ready to listen to my sincere apology." That will either get his attention or he will tell you to go to hell, but you will know where you stand with him. I'm betting that he'll call you within a few minutes of receiving that text.
Apologize now. He may reject it at this point if he is still angry, but it should go a long way to easing the tension between the two of you in the long run. If he needs a few more days to calm down, then at least he will know you are sorry which should help him calm down and keep the situation from getting worse. If you wait to apologize it will look less sincere.