Step 1: Accidently send a picture of my big cock to her phone.

Step 2: Get reaction over phone.

Step3: Beg her to come talk face to face

Step 4: Face to face gauge reaction, if she reacts negitavly swear it was for another girl and beg her to keep it to herself and plot fails.

Step 5: If she seems like she liked it in anyway for example jokes, laughs, flirts anything of those manners react back with same mood.

Step 6: sexually joke with her, touch her playfully  show interest.

Step 7: If it goes this far admit you sent it to her on purpose, then go for it all, if it works it works if it doesnt break down appoligize and beg her to not tell anyone. 

 Not the best plot if you have better message me very interested in hearing other ideas.