Re: help...key won't open gas tank
Another option to consider, though it may not apply to your bike:
I had an F4i key fail to open the tank lock when the bike was new. (The very first time I took it to get gas!) In this case, the key would turn, but it seemed not to turn quite all the way. I unbolted the cap and discovered that the lock bolt on one side didn't retract far enough to clear the lip to allow the lid to open. I ended up filing the tip of the bolt to shorten it (just a tiny, tiny bit). I lightly filed it, put it back on the bike, if it didn't work, I filed it again... until it finally worked. I never had any problems after that.
It's not likely that your bike has the same problem, but no matter what the problem is, it will be easier for you to figure it out if you unbolt the lock and cap from the bike so you can see what happens when you turn the key.