That appears fairly normal. The OS image is in a Recovery Partition, probably the last one on the drive which is around 8 GBs.
Now that you have updated, a Recovery Drive would not encompass the image for 8.1, as far as I know. If you want to revert back, best to do that in the first 29 days through the recovery process. If the option to revert back has already been removed, use whatever you can.
Personally, I imaged my system to a new mSATA drive and put the original one in a safe place..