I just wanted to give, perhaps, some reassurance until your scan. I know when I was in this position, both with the following story and with the subsequent MMC of my second, I liked a bit of hope to see me though.
So, I conceived my DD via a Frozen Emrbyo Transfer. I got my positive test at the equivalent of 9DPO.
I had some very slight spotting and called my clinic who suggested it may have been some irritation from the pessary progesterone.
Then, around 5weeks 5days, I had a massive bleed, similar to how you described, and I was absolutely heartbroken.
The clinic wouldn't scan me, being less than 7 weeks, but I also had a horrible dragging feeling and, crucially, some left sided pain.
So they suggested I take myself to A&E to rule out an ectopic.
So, 11pm, off I trotted to the nearest A&E, absolutely certain it was over. The lovely gyne doctor examined me to find my cervix closed, then took pitty on me and performed a scan with a big fat warning about how we might not see anything.
Little bean was right there on the screen, heart beating beautiful, and next to a large SCH which was the cause of the bleed.
She's now three years old and the bleed had gone by my 12 week scan.
I have absolutely everything crossed for you on Friday and hope you get some answers. It's an awful place to be.