I agree with waking her up and telling her you were going out. She absolutely did wake up because.....pregnancy bladder.
And keep in mind her hormones are out of whack. I remember all too well blowing everything out of proportion while pregnant.
I think both of you did things wrong and when and if you talk open and honest communication. I also can guarantee she will yell and cry because....hormones! Keep your voice calm.
And im sorry this is happening.