Told my best guy friend i would see him tommarow but i cant what do i do?

I like this guy a lot and just talked to him yesterday and he was sooo looking fooward to hanging out with me tommarow but now i cant what do i do? I texted him and told him i was soooo sorry and explained but he ddnt reply! Im worried that he is upset with me! What should i do to make it up to him??? What should i say to him to let him know i really am not lying??? HELP!!!!!