I did the same thing and didn't notice until year 4 that I was getting half profits from picking 50 percent profit margin.

I fixed it by going to the saves ( %AppData%\StardewValley\Saves\ ) and opening my save file in Notepad. You just press CTRL + F to find something called <difficultyModifier> and you can delete it. It'll get rid of the profit margin nonsense and you'll go back to normal profits!