hcg draw 😟

Hi y'all! On Monday I was 14 DPO and I had my blood drawn at 11 am - hcg was at 78. They asked me to come back 48 hours later (so today, Wednesday at 16 DPO). I should be 4+4 today and my levels today (blood drawn at 8:30 am) were 157. Just about exactly double. They seemed concerned they weren't higher though and I'm going in on 6+6 for an early ultrasound. Donny numbers look low? I'm trying to get ahold of a nurse to go again Friday. I'm trying not to worry!!