Miscarriage or twins?

Hi, I knew I was pregnant but I didn't know I was having twins. I started to spot bleed and thought I was miscarrying so went to my doctor and had an ultrasound where they told me I wasn't miscarrying I was pregnant with twins. I don't know anything about HCG levels as I conceived naturally and never monitored them but I do know that with twins they are are supposed to be much higher than if you were pregnant with a singleton.