Overwater????
You didn't water enough! I see a little bit of damp mix right around the stem and the rest of it looks dry.
Let me guess. You took that cup of water poured it just around the plant and did not saturate the entire medium. That plant is drooping because the roots are trying to grow into dry soil.
Saturate the ENTIRE container and then let dry. It should take at least 1/2 gallon if not more as dry as it looks.
Then, NO water until the entire pot is mostly dry. Especially no little *sips* of water in between.
Did you even get that mix wet before you transplanted? If not, you're going to have a hard time getting it to absorb water. Think of a dry mop vs a damp mop and which absorbs water easier.
Wet