I have to agree with the others... your beta was done at 23dpo (17dp5dt). At 19dpo for me, by beta was 1885. I have a singleton.
But this doesn't mean you are not having twins. There are lots of women with low betas (look at Barbara!) to start then wind up having twins. And lots of us with high first betas and have 1. You have to take in how many days post ovulation you are, and in the case of identicals, when they split, etc...
but congrats on your BFP!
