Everything's sad?

That's looking a lot happier!

Personally, at this early stage I would not want to be removing dead flowerheads or leaves, especially seeing as the plants have had a little bit of a fright. I'd want to give them a week or so to get their roots down, some water in their stems, and then you can gently handle them to remove the spent flowers and sad-looking leaves....

 

Hi,

The fact its recovered so quickly makes me think its watering.

If the compost you added was very dry that will take up a lot of water and perhaps the roots were not getting enough.

Would not worry about digging it in again etc, just water the whole patch and give it a good soaking, the worms etc will take it all down into the soil naturally.

You only dead head when the flowers are fading to prevent them wasting energy on producing seeds.

Sometimes you can nip the buds/ flowers off if the plants are small and you want them to put their energy into more growth, but from your photo I would say leave them on, they look good sized plants.

 

My dear friend. Nothing silly about your actions so far. Please, please stop downing yourself. Believe me if we were all to be asked. Most of us have made exactly the same mistakes, not one, but time and time again.
Yes as Tetters says. There are composts and composts. In brief. Most of us turn to buying composts, bagged up conveniently. I have experienced being supplied with Levingtons MPC. (multi purpose compost) it was just bags of leaves. Tried some of B&Q stuff, just like floor sweepings. At this point. You will probably find that all commercially packed compost will state it contains feeds etc that will last...however long. Why do we buy compost. Most of us haven't got the space to make our own, plus that old adage. I want it yesterday. On this score. I recycle soil/compost from my garden and greenhouse. Bag it up let it sweat or leave it to the elements. For a general MPC I have found JA Bowers the best.
Yes my friend. When adding compost and or mulching. The application needs to be worked into the soil. Otherwise some years forward, you take out a spit and examine it. Wowee! it resembles a multi layer cake. Reason why we apply feed to our plants, why we mulch etc. This is all to enhance and enrich the soil. Then the plant draws what it wants from the soil.
Back to those sad looking plants. Always a step worth taking. Give them a few days of TLC, then if all seems to be lost. A bit of surgery. Never mind the outside leaves etc. Go for the center growth. Cut it out. The life, heart, pulse of any plant lies insid that node, where top growth meets roots. My friend gardening involves taking chances. Some risks we win, others we lose. My friend. It is not the end of the world. I wish you well and happy gardening.