gasing up AC

[burnout 180]

i bought a retrofit kit to replace the r12 freon in my AC system. i followed the instructions and the all the oil went in without a problem but when i disconnected the freon it felt to me as if the can was still full.

Have i done something wrong should i have had the AC and car off when i connected the freon or was i correct to have the AC on. Or does the ac system just take alittle bit of freon. Or maybe it was to much oil so their wasn't any space for the freon to go.

Any suggestions?

[burnout 180]

Also it is a 3oz can of oil and a 12oz can of refrigerant.