Hi Sunflower
Take as much time as you like with writing answers
1 In terms of something on my mind, it can have either a good meaning or a bad meaning.
2 Running through my mind is the expression of being anxious.
3 Bite the bullet means taking a chance on it.
4 Hanging over my head means that I can't get something out of my head.
These expressions were a little difficult. Thanks for trying though!!!

I've written the answers below.
ANSWERS
1 Something on your mind has a negative meaning. It means that something is bothering you. We often say this when someone is thinking about something so much that they can't concentrate very well on anything else.
2 Running through my mind means that an idea or thought enters your mind. Keeps running through my mind shows that the thought or thoughts are repeatedly entering the persons mind.
3 Bite the bullet means you decide to do something unpleasant. In this story, Anthony decides to find out what the boss wants to talk to him about. He thought it would be something bad.
4 Hanging over my head means that something is causing you to worry or to feel bad. In this story, the fact that the boss wanted to talk to Anthony was causing him to worry.