Should I test tomorrow am...advise please!

AF is due on the dec 31st. I got a positive OPK test on the 14th of December.  Do you think Saturday the 27th is too early to test?  I'll use FMU. I'm hoping to  get a positive test because it's my fiancé birthday and thought a daddy birthday card would be the perfect way to tell him. But I don't want to test too early and get disappointed another month.