Lab experiment: Enumeration of Leukocytes
First I'd make sure all the RBC were gone just by visually inspecting. What should remain are your WBC and platelets at this point, and platelets are tiny so you can probably count anything between 5µm and 25µm. So for me that would include basically everything I can see minus background or debris.

So the problem now is with quantifying your count. You should know what the volume of your blood is, and here's why: What you're doing with a hemocytometer is counting #cells in a given volume, but you also diluted your whole blood with 150µL before you counted. So for example if a drop is ~60µL, and you diluted it with 150µL your dilution factor is 3.5, and it's important because your cell density equation is 

For reference, you typically end up with 4-10 million leukocytes per mL of blood, however.