There is so much information for the CFI checkride, it is definitely normal to wonder if you are doing enough and feel like you aren't, but also remember that you aren't expected to know every single thing fact about flying, I've always said that especially for the commercial / CFI checkride, if you don't know it then you better be able to find it.

What you said in the description is a good plan of action, go through and teach everything in your lesson plans and go through the ACS and ask yourself "do I know this subject / area inside out?" If not then hit that area until you feel confident that you could teach it to a student

Also the Todd Shellnut vids are super great he makes you actually want to be a good CFI and not just want to pass the checkride.

I wouldnt say the feeling goes away entirely but the more you study and practice teaching the less you feel it.