re: I Know I’m An a-hole But How Big Of One Am I?

If you have to get somewhere, then you have to get somewhere. Still, given that it seems like you were able to get past her somehow, it seems like some variation of excuse me would have been better...
"Excuse me. I'm in a hurry."
"Pardon ne. I'd like to pass."

You could have passed her in similar fashion without any expectation of having to answer to her. And it would have been less brusque than telling her to "keep walking", which is impolite, even if you added "please" in front of it.

Similarly, in a grocery store, if someone is blocking you from grabbing something and for whatever reason you can't wait for them to move, it would be completely impolite to say, "Please move." At a minimum, you might say something more like, "Excuse me. I'm just grabbing a can of __", as you reach in front of them.

The rudeness specifically comes from bluntly telling someone what to do / giving them a command (walk, move, etc.). It is most polite to wait if possible, but at a minimum, you should announce your intention (sorry, comimg through) and do what you have to do without telling them what to do.

The woman's weight is incidental. Your choice of words matters regardless. If you would like to see people being more aware and better mannered in society, then understand all of our interactions matter. And we should all hold ourselves to a higher standard.