50HCg at 10/11DPO is perfectly normal, that's not a sign of a failing pregnancy at all.
https://americanpregnancy.org/duringpregnancy/hcglevels.html
"3 weeks LMP: 5 50 mIU/ml
4 weeks LMP: 5 426 mIU/ml
5 weeks LMP: 18 7,340 mIU/ml
6 weeks LMP: 1,080 56,500 mIU/ml
7 8 weeks LMP: 7, 650 229,000 mIU/ml
9 12 weeks LMP: 25,700 288,000 mIU/ml
13 16 weeks LMP: 13,300 254,000 mIU/ml
17 24 weeks LMP: 4,060 165,400 mIU/ml
25 40 weeks LMP: 3,640 117,000 mIU/ml
Non-pregnant females: <5.0 mIU/ml
Postmenopausal females: <9.5 mIU/ml
"