Have you had this experience?

Katie🐢 • Single momma of a beautiful baby boy 💙 09.29.16
This is my first pregnancy and I am 5w2d. On Monday, the 8th my HCG levels came back 309. Wednesday 590. Friday 700. Today, Monday, 1477. They aren't quite doubling as they are supposed to. I go back on Wednesday to check again. I am almost convinced that I am going to MC. Has anyone else had this experience? 
Any guidance would be greatly appreciated!