G Code For Drilling Circle

I am a total newbie to all this and could do with some help please, I need to make an indexing plate on a cnc router and could do with some help checking the code below
%
O1000
(DIA 20.0 END MILL - NO CUTTER RADIUS COMP USED)
(MACHINE OUTSIDE OF DIA 100.0 CIRCLE)
(CIRCLE CENTER X20.0 Y30.0)
(STARTING CUT AT 3 O'CLOCK)
N1 G00 G17 G21 G40 G49 G80 G94
G91 G28 Z0.0
G28 X0.0 Y0.0
T01 M06
S2000 M03
G90 G54 G00 X82.000 Y30.000
G43 Z10.000 H01 M08
G01 Z1.000 F2000.
G01 Z-5.000 F100.
G01 X80.000 Y30.000 F600.
G03 X80.000 Y30.000 I-60.000 J0.0 (G03 I-60.000 J0.0 Works as well)
G01 X82.000 Y30.000
G00 Z10.000 M09
G91 G28 Z0.0 M05
G28 X0.0 Y0.0
M30
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I am hoping this will cut a 100mm circle from 3mm engraving brass