You'll be fine. UCD is basically shut down for the holidays right now (we start back on the 2nd), and they're not going to fault you for not abiding by the 'two weeks' thing. Especially not when they tend to be a bit on the disorganized side.
Definitely go ahead and call them on the 3rd when they said they'll be open. I'm sure everything will be fine. . .it's not your fault they hit you with the acceptance right in the middle of the holiday season.
Anyway, congrats! I know it won't be possible to relax about it until the letter is in your hand (for the record, they send you a letter and some forms to fill out; medical forms and a residency form, I believe. Don't be like me and wait to send those in. . .I forgot about 'em till July!!), but do try. It'll all work out I'm sure.