With no previous cycle experience, you don't know how you will respond - so I would start easy, even though you are over 200 lbs.
Go 10/20/20 and adjust as needed. Make sure your diet is in line! Three weeks is a bit short, by the way...
I will assume that you have done your homework, otherwise this will all be for naught. Don't forget about support supps.
Good luck!
R