Hi StormYZ and welcome to the forums!
Since you're asking to edit your save file I'll assume you know where to get it and what to edit it with. OK and to make a backup of that folder first! If not, lemme know and I'll write up a step-by step for your computer (PC/Mac).
Profit margin is set by the term difficultyModifier and looks like this in your save file:
<difficultyModifier>1</difficultyModifier>
The number is the relative difficulty, yours is set to .50 or similar, just change it to 1 and you should be set. I found this listed in both of these files in my Farm save folder:
SaveGameInfo
FuturePrfect_359069627
So I'd change it in both places. The Farmname_1234567890 file is big so may take a few seconds to open, be patient.