Diluteing test e

[Lil_bodybuilder]

I have 20ml of 300mg per ml test e. Now i want to cut it down to 250mg per ml. . . To do this. By my calculations i need to add 3.34 ml of oil. . . . Is my calc correct?
And what oil do i use? Cottonseed?
And how do i go about doing this. Do i just add the oil to the 20ml of test e? Thanks for the help.