Should you use English or (possibly broken) Japanese in Japan?

So I'm going to Japan next month with friends, and I'm the only one speaking reasonably good Japanese. However, I am really nervous about how to approach people when, say, buying train tickets and such.

I seem to have a perfect Japanese accent that easily misleads people into thinking my Japanese is very good. I can understand clearly spoken Japanese quite well, but would constantly stumble and use "correct", but completely unidiomatic expressions while speaking. In fact while trying to practice speaking unscripted Japanese, I find that I would make ridiculous gaffes, like mixing in Old Japanese (too much ancient poetry and linguistic papers for me!) conjugations and using the inappropriate/an inconsistent politeness level. Obviously I'll practice more, but in short, I sound weird, incomprehensible, and with a good-sounding accent trying to speak long sections of Japanese. Being Chinese (and thus somewhat passing as Japanese in looks) would, I imagine, add to the confusion.

OTOH, I hear that Japanese people have trouble speaking English. In fact, on many websites of hotels, etc I find that the English version's grammar is so horrible that it is near unreadable. So I'm also nervous using English and embarrassing somebody who has poor English.

How should I get by? In both cases, I would understand the other person and vice versa (with some difficulty). Do Japanese people tend to be embarrassed if they are unable to reply to a question in English? Should I imitate a moderate Chinese accent when speaking Japanese?