Let's buy orange instead.

Let's go tomorrow instead.

I'm not gonna be able to make it. (아무래도 나는 못갈거 같어)

Are you ready to go shopping ?

Hope you don't mind but
 I can't go (양해해주기길 바래~)

you are ditching me for a guy

죄송하지만 제가 먼저 왔거든요.
Hope you don't mine but I got here first

내가 먼저 왔다
I got here first

내가 먼저 가야겠는데요.
I guess I have to go first

컴퓨터를 바로좀 써야겠는데요
I need to use computer right now
AND