australia → oosutoraria
haha wa, yonjyuusai de, chuugoku de umaremashita. → haha wa, yonjyuusai de, chuugoku de mo umaremashita.
watashi wa yin desu. → watashi no namae wa, yin desu.
i've done this because of the context, but it isn't essential.
watashi wa chuugoku de umaremashita. demo, oosutoraria jin desu. → chuugoku de umaremashita ga, watashi mo, ima, osutoraria jin desu.
watashi no kazoku wa kami no ke ga kuroi desu. → kazoku no minna wa kami no ke ga kuroi desu.
tagai → takai
watashi no petto wo katte imasu. → watashi wa, petto wo katte imasu.
here, if you've learned how to yet you could make use of relative clauses, 'as for the pets that i keep...' ... 'watashi ga, katte iru petto wa...' and continue on with what you have to say about your dog, but i'm afraid i can't make out the first sentence about it.
you've written: "my dog's height is short. but the dog's eyes are big. the body is small. the dog's nose is long. but its ears are big. my dog is pretty."
you've used a lot of complete sentences to describe your dog's features, but because this is a little long, i've contracted it using -ku te, which enables the linking of adjectives, and re-arranged it slightly. i've also assumed that by 'tagai' you meant 'nagai'.
my dog's short, and has a small body. the dog's eyes and ears are big, and its nose is long. my dog is pretty. → inu wa, se ga hikukute, karada ga chiisai desu. me to mimi mo ookii de, hana ga nagai desu. inu wa kirei desu.
"一day" → tsuitachi (+desu).
lastly, you've inconsistently used kanji, which shouldn't matter as this is a speech, but it's something to note. this includes watashi, chichi, haha... and don't forget australia is oosoturaria, or オーストラリア.
