You really do a good job! :)

Most of your sentences are correct, so I just refine several words, and explain why it is better.

这个花园是私立的。 

》这是私人的花园

Although your sentence is grammatically correct, but we don't use "私立" to describe a garden. We would say 私人的.

》我总是很准时。

When we say "準時", it has already included the meaning of "arrive in time or on time."

So we don't say "到得" two words.

However, if you want to express you finish your homework on time or finish tasks in time, you have to write down. 

我准时完成作业。

我准时完成工作。

这个香蕉是成熟的。

》这个香蕉已经成熟了。 or 这个香蕉熟了。

Still, it is a grammatically correct, but we don't say it.

Most of the time we use "熟" not "成熟" to describe things,

but if we describe a person is mature, we definitely use "成熟"

Like, this girl is really mature.这个女孩很成熟。

我不喜欢酸的东西。 (good!)

这个房子是脏的。(good!)

印度很美丽。(great!)

意大利是阳光从足的。

》意大利阳光充足。

I find that many Chinese learner tend to use "是" in a sentence.

however, there is a great point is that in many circumstances, we don't need to have a verb to form a sentence in Chinese. So I suggest that try to forget "是", especially when you describe something with adjective.

太多是过分的。

》太多就超过了。 or 太多就过分了。

It is describe when something grow "to a certain extent", and it would be bad. So we use "就"

我不可以看懂，是不明确的。

》这个不清楚，我看不懂。

This is not clear, so I can't understand it.

"cannot"

1. = not able to do something, we say "不能" or "不会" in Chinese

2. = don't be allowed to do (maybe due to some condition or people), we say "不可以" or "不行" in Chinese.

But "不懂" has already included the meaning of "cannot understand", so we don't use 不能 or 不會 into this sentence.

今天天气非常好，是无云的。(good!)

》今天天气非常好，万里无云。 （better version)

对我女朋友我很温柔。

》我对女友很温柔。

玻璃很易碎。（good!)

》玻璃易碎 or 玻璃很容易碎 ( different sentence in the same meaning)

这个花园是私立的。

请你修改我的句子 :-)

请你修改我的句子 :-)