Yes, if you start wrongly then it's OK to make light of it and start again. But if you make a mistake in the middle, it's best to carry on as if nowt has happened - but I guess there must be limits as to what you can get away with.

I mentioned in another thread, that in a gig last Saturday, I misunderstood what we were going to play next (it was a tune), and thinking it was a reel, I started playing the chords at a fairly fast speed. It was only when the fiddlers started that I realised I was playing the chords for a different tune (normally played more slowly, but fortunately in the same key and same time sig i.e. 4/4). So I just played the right chords, but by then, faster than usual, while the fiddlers played faster to match the speed I had started at. It sounded fine, and we all had a laugh about it while playing, and I don't think anyone else there realised there'd been an error.