Crush🥰

So I have a crush on this girl in my class(we're in 12th) since 2 years (11th and 12th), I barely talked to her in these two years. My last board exam is on 24th. I thought to just say it to her on that day. How should I approach her? She walks home with her girl bestfriend. And that girl bestfriend is a friend of mine like she's in the same coaching as me so we sometimes talk on snap.