plant extract stock is 10 mg/mL from which I pipetted 20, 40, 60, 80, 100, 200 uL and made up to 3 mL using methanol

then i added 1 ml of 0.004% dpph solution (dissolved in methanol) incubated in dark for 30 min and OD was taken at 517 nm

Blank was only methanol

Control was 3 ml methanol+ 1 ml Dpph solution

My absorbance for control was lesser than the samples and also absorbance of my samples were increasing actually which has to be decreasing.

What may be the problem? how can i correct it?