Recently me and my gf went to hang out for a day.
But there i saw a sexy girl and started starring her, which my gf noticed and is now angry on me.
I know i did a way huge mistake, but i don wanna loose her, she have not talked to me since 2 days now, she not replying my messages and phone calls.

Start with an apology and maybe send some flowers. Let her know it'll never happen again.