Been there mate. You can talk openly, you just need to slow down in the moment and consider it properly, instead of discarding immediately as "vulnerability = bad". Do it now. Message and say this shit. And for future, rejection doesn't have to be humiliating. The way you handle it is the main factor that decides that, imo. You're just a guy that likes a girl.. a story as old and honest as time itself.

Also you prob didn't ruin her christmas lol.. not to be a downer but if you have 1 girl interested, that girl prob has 5+ guys interested. Is what it is. Just get to her before someone else does!