Hi, I've been working on my fuel tank for a while and I have it how I want it to be, however I have some problems that I am not understanding the reason why I am having problems.

I am concerned about symmetry, even though I have taken care to make sure everything is symmetrical by using the mirror tool where I can in my sketches, when I introduce a fillet it seems there is a small problem on the right back edge of the tank.  When I look for the Symmetry Check tool, it is not available to me and I am not sure why.

Another way I could check symmetry would be to flatten parts and check them that way but I am unable to flatten any parts either.

I would appreciate any help please.

Thanks, Daniel.