No need to panic, just reformat it
How to Fix Your USB Drive Showing Wrong Size on Windows (with diskpart)
If your USB drive is showing up on your computer as the wrong size, it is likely the result of the drive not being formatted correctly. Instead of the actual 16GB or whatever size your USB drive is, you will see something like a few hundred MBs available on the drive.
If you see that, don’t panic because your drive still has the original amount of memory space available. There could be several other reasons too, like your computer might be infected with a virus.
Either way, reformatting your USB stick should fix the issue and allow you to use the full available space on your stick.
