What should i do to stop the tect box appear every time i eject

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Hello, I'm Cherry!
I had a hard time ejecting my USB Flash Drive. This text box always appear every time i want to eject it, It says

"New Volume (F.) is in use. Save any open files on this disc, and then close the files or programs using the files before trying again. If you choose to continue, the files will be closed, which might cause data to be lost".

But i already closed all the files, and try ejecting it again and yet it was still not working.