Those Answer OPKs give false positives (for days and days on end) to most women and are very unreliable. Get some CB digital OPKs or First Response OPKs are okay too. If you don't conceive this cycle, I highly recommend Wondfo OPKs from amazon.com
As for BDing, as long as you aren't BDing unprotected without 4 days in between each time, there is no way you can BD too early. Timing doesn't sway so it doesn't matter when you BD; what matters is how often/much you BD in your fertile period (3 days before O + O day, so 4 days total). Thus why when OPKs don't work reliably and/or your having a wonky cycle, as those after a miscarriage often are, BD every 4 days is the best way to sway pink and get pregnant. Apps that tell you when to BD based on just your cycle length are not accurate for many women, even those with very regular cycles. My cycles are usually 28 days but I O anywhere from CD16 to CD20, and it's not at all predictable.
There is no way to predict when you will O, and as I've said, very often for at least a few months after a miscarriage your cycles will be strange - shorter, longer, Oing much earlier or later than usual, anything is possible. Thus why BDing every 4 days is best in your situation - bc no matter when you actually O, you will have just one attempt in your fertile period, which is the strongest pink BD tactic.
Since you BDed on CD8, wait until CD12 to BD again, then again on CDs 16, 20, and 24. I strongly recommend you BD on all those days exactly, regardless of what OPKs or your other fertile signs (CM, cervix) indicate, as those signs which aren't very reliable in terms of determining O under notmal circumstances anyway, are also likely to be atypical & misleading after a miscarriage. CD8 is a great day to start BDing on when using the every 4 days method, in fact it's what I'd recommend to most women, regardless of when they think they will O.