My FTC does not visibly open when I use the interior latch.

It does open, but the interior latch has to be pulled up while the gas attendant pushes in on the opposite side of the opening.

Now the cover is not completely flush with the body of the car, though it sticks out ever so slightly, it's just enough for the attendants to think it is released, prompting them to try and pry it open if I am not near my car to tell them that it requires a group effort to expose the tank!.

Don't know if this has any bearing on how to fix it, but two previous attendants attempted to force the cover open while it was frozen shut instead of de-icing the cover's edges first.

Is this an easy fix or should I just leave it be?

 

The door hinge has a spring the moves the door open when released. The spring can break.

Determine if the door spring still works to move the door open.

 

As an good news/bad news update, I bought the part that opens the door @ Toyota (under $5.00).

I saw a video on YouTube for a DIY part utilizing one of those black metal binder clips instead.
I got a pkg. of 6 or 8 assorted sizes at the Dollar Tree.

I started to remove the original one by prying it with a slot screwdriver. He mentions that the spring on his part was broken/missing. Although I didn't look for an actual spring in my unopened part, my original part must have got flattened out through age, because it now works like a charm since the prying!

The best answer I can come up with is I unintentionally pried from the opposite side of the clip as shown in the video which opened it up more so now it make contact with the door?

The bad news is I so wanted to see if that binder clip worked! It looks like it should.
As the clip states, the outside grip needs to be bent slightly outward to make better contact with the door.

Anyway, here is the binder clip YouTube link if anyone else has this problem: