|Microsoft's Windows software does not allow you to delete partitions on flash drives or memory cards.|
Formatting the drive in Windows won't cure your capacity problem.
Your problem was probably caused by you NOT clicking on the Safely Remove Hardware icon in your Taskbar in Widows and STOPping accessing the drive before you unplugged it while Windows was still running, or similar on your MAC.
You can use any of several programs to repair the FAT32 partition related data damage that is causing the capacity problem.
Troubleshooting USB device problems including for flash drives, external drives, memory cards.
See Response 1: