I was able to get a nice score on two different bottles and shifted from hot to cold water 5+ times without any luck. Do you have any suggestions?

The best method I’ve found is to get one good etch in the bottle, then slowly go over that etching with a lighter. Go all the way around, doing your best to only heat the mark. Once finished, plunge bottle into cold water. It should come right off.
It’ll take a few practice bottles before you stop getting uneven / cracked bottles.