Q:

Number of possible isomers (including optical/geometric ones) with C4H8O molecular formula

I found 32 isomers but I think I made a miscount.

Chain alcohols: 6, chain ethers: 5, and chain carbonyl compounds
(ketones/aldehydes): 3
Three-member ring alcohols: 7, three-member ethers: 6 (including ones
that have the ether-bond outside the ring)
Four-member ring compounds: 4, five-member compounds: 1

(Note: Enols are not counted because they're unstable)

A:

It would have been nicer if you included the isomers what you have been counting. However, based on the isomer counts, I assumed you are in correct track but originally thought you might have counted meso-isomer twice (as two stereoisomers) for the total count. Thus I drew all possible isomers and listed accordingly: 

Consequently, I also counted 32 isomers (same as yours). When compared to your count, I realized your count of chain alcohols (6), ethers (5), and carbonyl compounds (3) are all correct.  
However, your count of three-membered ring alcohols (7) and three-membered ring ethers (6) are incorrect. There are only 6 possible three-membered ring alcohols (one less than your count) while 7 three-membered ring ethers are possible  (one more than your count; see the chart). Therefore, it might not be the miscount of meso-isomer (if this is the reason, you should count 8 possible three-membered ring ethers), but be an error on structure drawing.
Your final count of for-membered ring (4) and five-membered ring (1) ethers are also correct. Precisely, only 1 four-membered ring alcohol is possible. 
Conclusively, you and I both have the same structure count but wrong counts on different kind of structures. You can compare your drawing with attached chart here and find out where you made the mistake.

