Assignment of contract agreement

[Alicia England]

Hey everyone, 

I got an investor interested in a property I have under contract. They are offering 13.5 and I have the property under contract for 12.5. When I put in my assigment fee. Do I put that $1,000 is coming to me and the total purchase price is $13.5k? I feel like that is low for my first assignment fee compared to what most are saying they mad on their first deal. I tried to use a agreement contract I downloaded  from a link on a YouTube i watched but it confused me more than anything. I'm just trying to figure out where I add my fee and if it's on top of the agreed purchase price or not. Thanks