How did you get that pic? Was that taken during the transplant process or did you rip it out, right now, to take that pic?
The compost you mixed in, was it aged? Did you make it yourself, or buy it from the store?
It could be transplant shock. Just have to wait a few days. It sounds like you did everything spot on. You soaked it. Now let it dry out for 2-4 days. Do not add fertilizer or anything else.
You can water it after 3-4 days when the soil is dry.
Can you show another pic of the plant in its spot right now?
My zucchini plant got "floored" during transplant, but peeled up on the 3rd day. It took this long because I forgot to water the soil!
And like I said, it picked itself back up.
One more question. The leaves, are they dried and crumbly? Or healthy feeling but just droopy?