yep, a lot (if not most) of us were raised to clean our plates. Wasting food is sinful even! My husband's family were very poor when he was growing up and you ate what you could when you could and as much as you could. Now that we're not poor well... it's really pretty dangerous to have that mindset. My family wasn't as bad off but my mother's family was so "wasting food" was a terrible thing to do.
I managed to break that cycle with my own children and grandchildren - they have to taste something new and eat a reasonable portion of their meal (I have had several try the "ok, I'm done. What's for dessert?" trick). Serving up appropriate sized portions takes practice too.
Being more than a year out, I don't have trouble gauging my portions nor do I have trouble throwing food away. It takes practice (hey, we get to practice several times a day!) and conscious eating.
I used to clean off OTHER people's plates too. Then one day I realized the truth that I am NOT a gabage pail. Sounds silly, but that is exactly how I was treating myself.
Keep at it!