Playing Zelda Link to the Past and got stuck in Dark Palace. help please?

For reference, here is exactly where I am:

http://www.zeldadungeon.net/Zelda03-a-link-to-the-...

Go to the 10th paragraph/picture set. I'm try to get through this northwest door going left.

Ok so I got stuck and directionless and looked up the ZeldaDungeon walkthrough online. From this I have managed to "diagnose" the problem: somewhere along the line I managed to waste a Small Key on the wrong door. Now I cannot progress past this certain locked door but have no access to any more Small Keys. I have gone to every Small Key location listed in the walkthrough so far, but every chest is already open and empty from my previous misguided (well, unguided) attempts. And all this is unfortunately recorded in my game save so I can't just die and go back and have it all set right.

Is there any way to salvage this without deleting my entire game save and starting at the beginning?? I know I'm not even halfway through, but it's a massive game and (especially being a gaming newbie) I've already invested many hours in getting to this point. I don't want to have to start over after all this. Please help me!

Thank you!