A couple of things
First, the "funky bittery, acetone-ish" flavors are most likely fusel alcohols that yeast likes to throw off when it's under stress. One way to prevent this is to make sure it has enough nutrients (particularly nitrogen). In the mead world, this is usually resolved with the addition of nutrients such as Fermaid K and diammonium phosphate (abbreviated "DAP"). I'm not sure if this is common practice with simple ciders, but I could see it being an issue if a yeast has high nutrient requirements or if your unfermented juice/cider is particularly low in nutirents.
High fermentation temperature is another common contributing factor to fusel and general "off-flavor" production. According to the information on the White Labs website, WLP775 has a preferred temperature range of 68-75°F (20-24°C).
Basically, like mead, the best cure for that fusel alcohol burn is time.
As for the cider going dry, the faq section of the White Labs WLP775 page puts the alcohol tolerance of that yeast around 12%. Right now, you're sitting at about 7.56%. If you want to sweeten it up, you could always stabilize and backsweeten. If you backsweeten with some apple concentrate or extra juice, that could provide a little more apple flavor and acidity, depending on how much you sweeten. If you add it without stabilizing, though, then your yeast is just going to chew through it.
Finally, if you wanted to "sour" it up, you could add some acid blend (or lemon juice, I guess) to taste.
Overall, though, it sounds like you just need to let your cider age a bit. I would give it a few more months for the flavors to develop before declaring it a failure or a success.
Update
I found a pdf from the Northern Brewer that hits on some of these points.
https://cdn.shopify.com/s/files/1/2785/6868/files/cider.pdf
On nutrients:
Add yeast nutrient. Wyeast Wine or Beer Nutrient, or generic
Yeast Nutrient. Roughly 1/4 tsp per gallon is a good starting
point. Be prepared to add more once fermentation is well under
way
On acid additions:
OPTIONAL: Add acid. Most juice, especially juice made from
later season apples, will have a lot of sweetness, but little acid.
Acid helps to balance the cider by adding sharp, crisp character.
Small amounts of malic acid can be added to taste, up to
one tablespoon in five gallons. To ensure more accuracy and
repeatability, consider measuring the pH or using an acid titration
kit to determine approximate acid content. Remember,
it’s always possible to add a little more, so err on the side of
caution
There's actually a lot of good information in the document. If you plan on making more ciders and meads, it would be worth taking a quick look at it.
