I am not good with AC work

I had to play with it. My mechanic put 28OZ of R134 as a retrofit, 1984 300d. he said that was 80%. I am pretty sure that the the R12 capacity is 1.2 Kg which is 43 0z which 85% of that is 36 oz. so i wanted to put more r134 in to make it run cooler. I read the instructions and added about another 10oz, Duh. the next day it kicks off while running due to high pressure i assume.
I dont want to go back to mechanic and look like a fool. Can I empty the system and put in three cans 36oz and feel good about myself (enviromental reasons). If I can do i release the coolant from the low end or the high end or both. and what do i do about the 8oz of oil he put in there. do i need to replace that or does it remain in the system.

Or should i just go back to the mechanic
(I only paid a mechanic three times in my life, I dont like it)

Thanks for your help and have pitty on a beaten soldier of auto maintenance

bob

PS even my wife is mad at me and she is very understanding