“No, it's just a scratch.”
You cut your finger. Your sister wants you to put some medicine on it to make sure that it doesn't get infected. You say this because it's only a little cut and you don't think that's necessary.
No, it's just a scratch.
"A scratch" is a very light cut. You might get "a scratch" if you
- bump into the sharp corner of a table
- fall off of a bicycle
When you get hurt or cut, you usually check to see if the cut is deep. If it's not, you can use this phrase.
A: Is it serious?
B: No, it's just a scratch.
Talk about something that's not very important, not interesting, not a big problem, or not hard with the word "just". For example:
It's just a short trip. I won't be gone for long.
This is just a temporary job for me.