I am just wondering how bad am I affected by it? The cutting board isn't destroyed just a couple of shavings from the burn. I placed it on a very hot range and it got melted for a few seconds.

Is melted plastic the same as burned plastic? It gave off white steam/smoke for a few seconds not black smoke. The board wasn't smoky just the range (it's not a gas range)

I did this several times already with grocery store plastic bags... it gets hectic sometimes I get careless with two young children crying and runnign while I need to cook.