Percentile-wise, a 770 doesn’t look great. Regardless, is it still a good score?
Yes, unless you are planning for MIT or Caltech.
Don’t get caught up with percentiles. It is important to understand that for several subjects, the percentiles are depressed because so few colleges request Subject Tests, that the ones that do are the ultra selective ones. As a result, it is the high achieving kids taking the tests. No AO is sitting on the floor cross-referencing scores with percentiles.
You might be disheartened because you are not be used to see yourself in 60’s percentile. But even perfect 800 score is about 79th percentile only. But the correlating score of 770 is what matters. Only very strong students took it and you are on the better half among them.