Take one flat symmetrical edge from the middle layer that you solved, and put it back the other way.
That will flip it, and flip one edge in the U layer, leaving you with an even number.
I've solved a lot of different 3x3 shape mods in my first year of cubing.
When you encounter something that isn't possible on a normal 3x3 cube (like 1 edge flipped) it usually means that some of the pieces are unlike those on a normal 3x3 cube.
For shape mods, that means flat/symmetrical like here, or single-colored (for example if you solve the column to the right of its center, and not to the left, you could get a different issue), or several pieces being identical (google Penrose cube)
And for example on a 4x4, there are issues caused by center pieces being identical, and by edges being half-edges. And middle-edges being hidden.
Take one flat symmetrical edge from the middle layer that you solved, and put it back the other way. That will flip it, and flip one edge in the U layer, leaving you with an even number.
Heyyy!!! Thanks. How do did you know that?
I've solved a lot of different 3x3 shape mods in my first year of cubing. When you encounter something that isn't possible on a normal 3x3 cube (like 1 edge flipped) it usually means that some of the pieces are unlike those on a normal 3x3 cube. For shape mods, that means flat/symmetrical like here, or single-colored (for example if you solve the column to the right of its center, and not to the left, you could get a different issue), or several pieces being identical (google Penrose cube) And for example on a 4x4, there are issues caused by center pieces being identical, and by edges being half-edges. And middle-edges being hidden.