I screwed things up with someone who is dear to me, how can I fix it?

So this boy and I "used" to like each other, we were best friends, we had a small fight one day and I stopped talking to them, recently the messaged me saying how sorry they were but I didn't answer, I just left them on read, this was on christmas day, since them I've been thinking what to say, is it too late? what if they hate me now because I didn't answer?, what should I tell them?, should I use an excuse of why I left them on read?, what excuse should I use? Ive been also drawing and drawing stuff that I could maybe send them as a sorry since they would always say they loved my art, but for some reason I can't seem to get myself to send it.

So.

If you have any idea of how can I maybe fix this.

Please tell me!