So, I was playing Moonlight Sonata and there are some parts that require awkward hand positions, I think everyone experiences that with this song, but after playing my hand feels weird and I went to play another song and I find myself missing notes I don't usually miss. It's most notably because of the part where your pinky reaches out to the right to reach that G note while you're doing triplets with the same hand. I do stretch my hands almost everyday and can do a 9th fairly easily. Is it just something your hands need to adjust to? It's kind of an uncomfortable feeling.

I can't help but think of "N64 thumb," for anyone familiar with video games, which some kids got (sorry, but dumb kids, i never did this) from stretching their left thumb all the way from the center of the N64 controller to the D-Pad on the left because they couldn't figure out to just move their hand. A few people I know have a weird thumb on their left hand where it sort of dislocates itself.

If you think of it as stretching, you may be causing injury. Can you reach the notes without "tensing" or "locking" your hand in that position?

Yes in my edition there are a few uncomfortable stretches in Moonlight part 1 but they last only a fraction of a second. I think uncomfortable for a very short time is ok (just don't practice that single stretch too much to avoid injury).

I don't think I was tensing or locking into it. It was quite a reach though. I think I figured out the problem though.

My Index finger was on middle C# (if that makes sense) and my ring finger was on E then my pinky was reaching up to G#. I just realized to put my middle finger on E instead which gets me a little closer.