In general, I have to say it's pretty well written. However, the general vibe feels a little bit odd followed by some minor mistakes.
I believe 弄堂 is a Shanghainese word that stands for a specific street type only limited in Shanghai. Looks kind of like a back street in western countries but located within buildings. I'm sure you meant something else.
我觉得这是一个很善良的事儿。 <this felt really odd to put in a sentence in any language, feels like you are doing charity.
This literally translate to "I think this is a really kind-hearted thing to do." The closest meaning of 善良 I can get to in English is kind-hearted, but even that does not truly reflect the meaning of the word. This word is mostly used when describing somebody who helped the ones that are really in need, or gave away something that they really cherish to save others.
If you use it to describe somebody 善良, the characteristics that I get instantly is he often helps people, he's simpleminded(never thinks bad things of others), not sarcastic, etc.
As you're a foreigner, I assume the tutor of yours will accept it even it's odd. But we can make this work if we put it another way.
Because, I believe this is a nice thing to do, so I've cut small pieces of bread then threw it out to the pond to feed the fishes. (Chinese-like grammar translation)
所以没什么好事 < I don't understand. Literally means "So there's nothing good happened." Please rephrase.
Other than the above, very good!