Those carrying twins help!

So I went for HCG level and it was 170 initially. I went 4 days later (number should be 680 based on doubling every 48 hours) and my number was 878. Could I possibly carrying twins?? Or would the number be even higher if so?? What are your experiences with HCG and carrying twins? I am very early so I won’t have an ultrasound for a couple of weeks.