Hi & Welcome to HCM.
I can understand your concern regarding efficacy of Diane-35 as a
contraceptive.
Diane-35 (Cyproterone+
Ethinyl estradiol) is commonly prescribed to treat conditions like acne and hirsutism, while acting as a contraceptive (birth control pill).
To be an effective contraceptive Diane-35 should be taken from the first day of the
menstruation onward regularly at the same time for about 21 days.
Since you have taken Diane-35 three days after an unprotected sex and that too on anticipated ovulation day it may not prevent the unwanted pregnancy as it has no effect on
implantation of the conceptus if fertilization has occurred.
Moreover, Cypoterone acetate which is present in Diane-35 is a
progesterone with androgenic properties, and has virilizing effect on the female fetus.
So, in view of the above, there is every possibility of you getting pregnant.
Consult a gynecologist if your next period is delayed.
Hope this answers your query.