It was dark, and he knew what he was doing was dangerous. Not the kind of danger that gets more frightening in the dark, but that made it even more intimidating: there was no physical circumstance that could make things worse and so, he knew, there was nothing that could make things better. He was just going to have to screw up his courage and get the job done.

You didn't mention if you wanted someone to look over the whole thing, but I can if you are in no hurry. I just signed up for several reviews so my box is full. It will probably take up to a week for me to turn it.

POV switch
Your first paragraph is in John’s Point of view and the next is in Alice’s. Try to avoid such a thing in the future. A POV switch should be done with scene breaks. Do this opening from one perspective only.

‘was’ overuse
It is the most over used verb in writing. You used it ten times in these thirteen lines. You can usually find another way to write a sentence without them. For example…
She was very surprised to see John Adams standing in the doorway, holding a bunch of flowers.
Could be written…
Seeing John Adams standing in the doorway with a boutique of flowers startled Alice.
Seeing ‘was’ in every sentence will usually get a ‘thanks but no thanks’ from the assistant editor.

telling vs showing
Show whenever possible. Writing something like…
The dark room scared John is telling. John trembled as he felt his way through the dark room is showing.
Your entire first paragraph is telling. Show how John feels as he approaches the door with the flowers. We want to experience his discomfort. A shy young boy that has finally gather the courage to present the object of his desire with a gift of affection only to have his resolve crumble when he comes face to face with his beloved from afar.

withholding information
We don’t who the first paragraph is about, where he is at, why he is there, why he needs to frightened, why it’s so dark, and why we need to be there witnessing it. Clarity. It helps.

Than there is contradictory sentences such as…
there was no physical circumstance that could make things worse and so, he knew, there was nothing that could make things better.
It couldn’t get worse so therefore it couldn’t get better????
Show us what he is going through and not tell us about it. Here is another way it could be approached.

John set a foot on the wooden steps leading to Alice’s front door, careful not to make it creak, squeak, or doing anything else that may draw attention to his presence. Darkness covered the Rosetree’s front stoop, which relieved John. It hid his approach and helped him go through with his plan. He poked his shaking index finger to the doorbell. The ring made his insides jump. A half-a-minute later Alice Rosetree opened the door and blinked at John standing with a boutique of daisies in his hand.
He turned his head and jammed the flowers in her face. “Umm, ahhh. Al, uh.” Knowing he sounded like a fool he clammed up. Saying nothing for a good minute.
Say something, Dummy!
All coherent thoughts left him. What remained of his courage fled as well. With the primal fear of a gazelle being pursued by a cheetah, John ran from Alice’s step and into the darkness.

I will say though, as to the contradiction I wrought, I was merely trying to say that the situation would be just as frightening regardless of the circumstance, and that this in itself was a cause for discomfort. Apologies for saying it in the most convoluted and unfollowable way possible :P