There's a really wide range for a normal hcg value for both singletons and multiples, and a dark line can be present (or absent) in either case.
Go for an ultrasound dear
I had a very dark line that came up instantly, I had very high hcg and I knew multiples could be why but I was pregnant with one baby my little boy x
Not necessarily! You may have just implanted sooner or HCG rose quicker. It COULD mean twins, but it doesn't always mean that. The only way to know if it's twin will be your first ultrasound! Congratulations!!!