I cannot open the fuel fill cap

Your description sounds like the latch or the cable to it has failed. You can access it from inside the trunk area by removing the inner trim panel. From there you can have someone push the handle and see if it is the latch or the release. One thing you can try before that would be to have someone hold the release and gently pry on the door with a plastic bar or similar, it may be the release just isn't retracting fully and needs a bit of help. If it does come open that way you will want to lube the latch area and work the release a bunch of times to free it up.

Good luck. Usually getting to the latch is the hard part. If it is a bad cable the trim below the door needs to come out to get at that end. Then the trim next to the rear seat. Or you can do like I have and stuff the replacement cable down through from the rear compartment and guide it to the lever. I generally don't like this design myself because of the latches, they get moisture in them and rust and this is the result. Some part fails and you can fill the car.
If you have any other questions just shout. Honda doesn't show any real good images of the system, just a sort of sketch of the routing.
The part numbers are 74880-SDA-A01 for the 4 door and 74880-SDN-A01 for the coupe. Those replace the entire part for the gas door and the trunk.