hcg results

So i just got my blood test results back and its positive! The nurse said my hcg level was about 240 which was low but its also because im early into my pregnancy. Only 2 days passed my missed period. She said i would go back in every 48 hours to make sure my levels were doubling? And after about a week i should be between 1500-2000 hcg and could schedule my first ultrasound. Is this normal? Has anyone else had to do this? Its my first pregnancy so naturally im freaking out about every tiny thing