The vial is labeled either units, cc or both and should be labeled U-100 somewhere.
The vial and the syringe cannot possibly both hold 1 cc. Are you sure the vial doesn't say 100 units per cc.?
Ten units is 0.1 cc. Three weeks is 21 days, so you should have injected 2.1 cc
Other than that, I am confused by what you say.