Hello again, hetty;
I guess I'm still not clear on your situation; you say you are on Diamond Princess on April 16 but you are NOT ABLE to get a handicap cabin SO FAR. Are you booked and hoping to get a handicap cabin? Or are you hoping to book a handicap cabin? As Neil pointed out, most areas of the ship are accessible. But a regular cabin will present some real problems; you probably won't be able to get it through the doorway while seated, and you definitely won't be able to get it in the bathroom--there is a very high threshold and barely room to turn around while standing. And unless you have a suite, I don't see how you can maneuver around the cabin.
I think you really need to get with your travel agent and resolve this as soon as possible; I don't see how you can do the cruise in a regular cabin. I don't say this to discourage you; I just want you to know that you need to be sure you have a wheelchair accessable cabin.