hCG doubling is only at first - it does slow down a bit after a few weeks (can you imagine the work the placenta would need to do to double those figures? Making 10k U/L in 7 weeks then another 10k in 2 days is quite a stretch; I think it should be fine. So long as your hCG is still growing that's a good sign - have you checked out the "normal limits" in the sticky here?