What should I do?

Me and my friend have been together for like 5 years now. Today, I made a joke and they took it as an insult. I think I hurt them with it and I really want to apologise (I already did once but I feel like it might not be sincere enough or they just ignored it). I dont know if I can let our relationship just die like that because I really don't know what to do espically if our group will have to split up because of it. Please give me some advice ╥﹏╥