AS COOL AS A CUCUMBER // GOT IT IN THE BAG

• If you are as cool as a cucumber, then you are calm and untroubled by stress. 

• If you've got it in the bag, then you are certain you can accomplish a task.

Example

Max: Is Marie worried abou her finals?
Jim: No. She's as cool as a cucumber. She's sure she's got it in the bag.

image courtesy of dreamstime.com

FINE TUNING

If you "fine tune" something, you make small changes to improve it. This expression comes from the idea that we tune a musical instrument to make it sound on key.

Jack: Are you finished with your term paper?
Sue: Almost, but not quite. I still need to fine tune it before handing it in.

image courtesy of dreamstime.com