I Went In For An Early Ultrasound (6 Weeks 4

I went in for an early ultrasound (6 weeks 4 days) due to a having a previous ectopic pregnancy. I was also having severe cramps from a formidable UTI and possibly flatulence. The pregnancy measures exactly with my LMP. However, due to ultrasound measurements the baby was aged 2 days. The heartbeat of the visible singleton was 166 bpm. This seems high to me based on all the charts I've read l. My HCG levels were 61,530 at this appt. The day of my missed period the HCG levels were 287 and 45 hours later they were 673. By 5 weeks 2 days my HCG levels were 5200. I've been gaining 1 lb per week. Am I missing something? Or is this normal for a singleton? I'm wondering if someone may be hiding.