What do I do with this certain keyword in my amazon PPC ad? Very conflicted..

I feel like i have to tell you what im selling in this case.

I am selling stone coasters. They’re slices of geode rocks. Irregular shaped, natural edges etc…

The problem is the keyword “coasters” it obviously has the highest search volume so i bid pretty high on it. I have gotten almost 100,000 impressions and 272 clicks. My ACOS is through the roof on this keyword. I would love to lower my bid on it or even get rid of it and stick with the more specific words like “stone coaster” and others alike. The problem is “stone coaster” and others have not many searches/impressions and literally all of my sales have come from just the one keyword “coasters” any advice on how to handle this situation? If its the only one bringing me sales i feel like i need to keep it. But need to lower my bid my a massive amount with my conversion rate being only .02% (yikes). What would you experts out there tell me to do? The other, more specific words have very little impressions but the CTR is very high. Do i just need to swallow my pride..get rid of the keyword “coaster” and have sales come in slower with these more specific words? Help!

Thanks everyone for reading and giving advice. Hope everyone has a great week!