Then we went to the local botanical garden in our city.

"in our city" is a bit of a long phrase and so it's a bit unnatural to repeat so many times.

Instead, I sat in (on?) my e-tricycle and wrote this journal.

It actually kind of depends on the design of the tricycle if we would say "on" or "in" here.

"On" has people basically picturing a bike with three wheels, while "in" has people picturing something more like a cart with a bucket seat where you're low to the ground.

e.g. we'd describe it as "sitting on" for this kind of e-trike: https://i5.walmartimages.com/seo/VIRIBUS-26-Inch-Adult-Trike-350W-Dual-Chain-Electric-Tricycle-36V-10Ah-Coral_ddd04c91-573f-4dd9-9fa9-dd4df6625e49.cff8f27e1c0215414b648b9867000309.jpeg

But we could describe it as "sitting in" for this kind of e-trike: https://electrek.co/wp-content/uploads/sites/3/2018/06/electric-recumbent-trike-header.jpg?quality=82&strip=all (some people would still say "sitting on" though!)

I think the first kind is way more common, so probably you want "sit on" here.

While 24 degrees Celsius is a pleasant temperature for being outside, I evenstill feel a bit chilly.

It’s cloudy, with occasional light rain, so I feelt it’ was a nice day to be outside.

Be mindful of the tense you're writing in. Although the present tense isn't necessarily impossible, the past tense would more logical.

Instead, I sat in my e-tricycle and wrote this journal entry.

Just "journal" is understandable, but strictly speaking, I think it should be "journal entry".

While 24 degrees Celsius is a pleasant temperature for being outside, I evenactually feel a bit chilly.

"Even" doesn't strike me as an appropriate word here. I've switched it out with another more suitable word. If you wish, you can also just remove it and write "I feel a bit chilly."