High hcg level

Hi there. This is my 5th pregnancy, with a miscarriage 1.5 years ago. I am currently 6.3 weeks pregnant. I had my levels tested yesterday and the nurse called today to tell me there was no need to retest because my hcg was measuring at 118,000. She said thats high but good. I have to go in for my first ultrasound this coming Monday instead of a week from this coming Friday. What could be the reason for such a high hcg besides a miscalculation of dates? Thanks!