USB Drive not partitioning properly... or something.

1) How are you installing windows 10 on there (With what program)
2) If you are installing it on to that thumb drive using Windows to USB or Windows On the Go 8Gb is WAAAAAY too small. Need at least 32 really and even if it is a USB 3.0 drive it will be slow as hell (I know i tired it and then moved to a external hard drive which even on a USB 2.0 port is faster than my 3.0 USB because Flash memory have VERY low Random reads and writes unlike hard drives. You either have to get a USB HDD/SSD or a SSD Thumb drive which arent cheap.

3) You will need to use disk part, delete the partition, and then make a new partition in disk manager. USB drives aren't suppose to have more than one partition because they don't work with more than one.