Generally, questions amounting to "How good am/was I?" or "Was I performing OK?" do not make much sense in any context. Good questions are, for example, "Should I skip verse 11?" or "Did you understand the lyrics of ...?" – you may get helpful hints. Listening to your recordings will often help you with specific technical problems such as pronunciation, intonation etc.

Of course the question remains whether your audience is seriously disappointed, and just too polite to admit it. This is normally not too difficult to find out if you really try, using the above advices. Actually most audiences take delight in being generous (– not pitiful! –), unless they have very good reasons to expect an excellent performance, e.g. paid a large entrance fee or heard you boast. Accepting generosity with dignity is an art in itself, some Asian monks devote their lives to it.