I'm not one to go back to a restaurant and complain, but if the discrepancy was large enough I'd probably leave a review online

Maybe the restaurant was counting the pre-cooked weight and you're counting the cooked weight? Like I know when you order, e.g., a 1-lb steak from a restaurant that steak isn't going to actually weigh 1 lb... maybe 2/3 or 1/2 that...

Once you've paid for it you've had it. I wouldn't go back there ever again. You could report them to the relevant department if you think they're overcharging regularly.

Wow. They must be mad. They would never see me again.

1.5 pounds is nothing I eat more than that for breakfast

I would probably just accept it at that time, but I'm not sure. It sounds a little embarrassing to go back and tell them to change it if you'd already paid.

I would be a Karen and complain to management. Likely leave them a scathing review online.