I can't help with the regulations for a boat your size, but would recommend reaching out to your local Coast Guard Auxiliary and arrange a Vessel Examination.
This is a great courtesy service where a qualified vessel inspector comes to your boat and checks all the Coast Guard vessel requirements -- including fire extinguishers. There's no enforcement of penalties involved and you receive a Vessel Safety Check (VSC) sticker. Having one of these goes a long ways if you are boarded for a Coast Guard inspection.
Here is a link to the CFR. https://www.ecfr.gov/current/title-33/part-175/subpart-E. Scroll down and you’ll find the table.
I can’t figure out how to cut and paste the table without messing it up but I think you need a minimum of 3 20-B portable fire extinguishers if your over 100 but less than 500 gross. Didn’t see any reference to net.