Under no circumstances can you end up with half your car on the pavement, the general rule being that you should follow the highway code despite what other vehicles are doing. That being said, it was clearly a poor place to ask you to pull up on the right as it would be luring you into doing what the other vehicles have done. When pulling up on the right it is part of a manoeuvre and they will be expecting you to reverse, something which they wouldn't allow you to do on the pavement. If it was me I would probably have picked a different location/manoeuvre, or given some discretion.
There is some merit for a complaint on the basis that you have been asked to pull up on a narrow road where other cars are parked on the pavement, this is generally against guidance for this type of manoeuvre as it could be construed as luring you into performing a serious fault.