After plugging in HFS+ formatted USB stick, Windows sees a partition with only ~200 Mb size, when the initial size is much larger.
This happens, because Windows has issues with mounting removable drives, which have GPT partitioning scheme.
Firstly, back up all the necessary data from the USB stick on your Mac, because the next step will clear all the data on your drive.
Open Disk Utility (Applications -> Utilities), choose your HFS+ drive, and click “Erase”; choose Mac OS Extended (Journaled) and Master Boot Record in Scheme drop-down list.
Now you are having HFS+ drive with MBR partitioning scheme and you are free to return all the data to the drive.
If you plug it into your Windows PC with HFS+ for Windows installed, the mounting process shall go fine, and you will be able to browse the whole capacity through Windows Explorer.