I just happen to have my fluid dynamics book closeby.
If you really mean 5.5 square centimeters (a very small wing), at 45 degrees it is quite separated flow, of course. Also at 45 degrees, downforce will be about equal to drag. I get APPROXIMATELY .86 ounces of downforce - this will be a ballpark number.
Some assumptions are the plate is close to square shaped, and thickness is less than 10% of the edge length.