Why didn't Shouko confess her feelings to Shoya afterwards? At the scene where Shouko tries to give a plant pot decoration thingy, she tried to confess her feeling to Shoya, but it was rather interpreted as 'tsuki (moon)'.

I'm wondering now why Shouko didn't confess her feelings later?
After her initial failure, Shoko lost heart. Additionally, another opportunity never showed up.

First, let's examine what happened. Shoko finally felt comfortable enough around Shoya to try speaking aloud, and she changed her hair so that she could confess her feelings, but Shoya rejected her not once, but twice. The first time was by telling her to use sign language, even going so far to admit she sounded weird when Shoko asked. The second rejection came when he misunderstood her confession as meaning "moon". It really doesn't matter if Shoya genuinely was having a difficult time understanding what Shoko was saying; this outcome definitely hurt Shoko and shattered her confidence. This is evident when she runs home and throws herself on her bed, only communicates by sending two despairing texts to Yuzuru. She also went back to mainly using sign language to speak to Shoya. Supposing her romantic feelings even remained intact afterwards, she wouldn't be trying again for a long while. In her despair, she probably felt stupid for trying in the first place.

And then what happened? Soon afterwards, even more of their former classmates started showing up at the Tuesday meetings (invited or otherwise). Shoko was alone with Shoya a lot less often, so there were few opportunities to confess with him. And with what happened later in the story, Shoko became more preoccupied with her feelings of guilt, pushing any ideas of confessing far from mind.