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

Just message him a simple reply like "Hey, what's up?"

If he doesn't respond then that's that and move on. If he does, don't apologize unless he asks why you didn't text him back. Obviously it has been the Holidays so that's a legit excuse.

Be friendly, don't come out and tell him your feelings, guys tend to over analyze girl's feelings and make stupid decisions. Just be the cheerful girl I'm sure you are and ask him about his week.

You didn't screw anything up. It's just a text, not the end of the world.