考试：上海话

我用英文写，让大家看我原本的意思.
I'm going to write this in English to let everybody see what my original meaning was.

Today was my 8th class with my teacher on italki.
今天是我（跟老师？）在italki上的第八课。

It is okay to leave 跟老师 part out. 

We have reviewed 4 lessons that cover greetings, numbers, time, weather, and directions.
我们复习了四课包括致礼，数字，时间，天气还有方向。

Usually, class consists of my teacher reading the sentence in Shanghainese and my repeating what she said.
平时，上课就是老师用上海话念句子，然后我就复述。

You can leave the first comma. You can also write it as 平时上课时老师会用上海话念句子， 然后我复述 to sound a bit more natural. 

She will then point out any nuances between Mandarin and Shanghainese.
那么，她会解释普通话和上海话的出别。

Should be 然后 rather than 那么. 

Usually I know what she means, but since Mandarin is my 4th language, sometimes I do not.
大部分的时候，我听得懂。但是，因为普通话是我的第四个语言，有时候我不懂。
＊关于我母语，应不应该说《学》？我由小时候说广东话不过从来没有《学》过。

You can just say, "It is my 4th language". 

Today, my teacher wanted to test me on my progress.
今天我老师要看看我有没有进步。

She told me in advance to be prepared.
她告诉了我准备好。

她提前叫我好准备。 提前： in advance 

She chose some words and example sentences from the lessons and said them in Mandarin. I would try to say it again in Shanghainese.
她从课里选了几个词和几个例句，用普通话说出来。我就试着用上海话来说。

I failed miserably. :(
我完成失败了. :(
了 turns the sentence to past tense. 

Unfortunately, I studied all the frequently used words, but none of the folk sayings or example sentences.
不幸的是，我复习了常用词，没有复习民间常用俗语例句。

考试：上海话

我用英文写，让大家看我原本的意思.
I'm going to write this in English to let everybody see what my original meaning was.

Today was my 8th class with my teacher on italki.
今天是我（跟老师？）在italki上的第八课。

今天我和我的老师在italki学了第8节课。

We have reviewed 4 lessons that cover greetings, numbers, time, weather, and directions.
我们复习了四课，（内容有）or（包括）致礼，数字，时间，天气还有方向。

Usually, class consists of my teacher reading the sentence in Shanghainese and my repeating what she said.
平时，上课就是老师用上海话念句子，然后我就复述。

She will then point out any nuances between Mandarin and Shanghainese.
接下来那么，她会解释普通话和上海话的出别。

Usually I know what she means, but since Mandarin is my 4th language, sometimes I do not.
大部分的时候，我听得懂。但是，因为普通话是我（学的？）第四门个语言，有时候我不懂。
＊关羽我母语，应不应该说《学》？我由小时候说广东话不过从来没有《学》过。

Today, my teacher wanted to test me on my progress.
今天我老师要考考我进步了没有看看我有没有进步。

She told me in advance to be prepared.
她告诉了我准备尊卑好。

She chose some words and example sentences from the lessons and said them in Mandarin. I would try to say it again in Shanghainese.
她从课里挑选了几个词几个例句，用普通话说出来。我就试着用上海话来说。

I failed miserably. :(
我完成失败. :(

我做得一塌糊涂

Unfortunately, I studied all the frequently used words, but none of the folk sayings or example sentences.
不行的试，我复习了常用词，没有复习民间常用俗语例句。

不幸的是，我复习了所有的常用词，但是却没复民间常用俗语例句。