USB used as bootable but when I deleted from disk management the unallocated left is 8gb out of 32GB

Question

I used GPT bootable disk but didn't boot when I tried installing. So wanted to format the disk back to normal but can not format. So I went to disk management and delete all files in usb but the unallocated become 8gb from 32GB. I tried already dispart and clean but still left with 8gb. I have checked attributes but none is read only. Just wondering were the other storage space went. I have tried also the free partition tool but nothing happened and still unable to format after assigning drive letter.