Please help me to correct my writting and give marks for me

I think you should change a bit of the words... like this:

This year, our parents are planning to go to Guangdong.
If I go to Guangdong, I will go to the Cheung Lung Water Park. lt is because it is an exciting place.
The website of the water park says that the Tornado is like a big horn.You
can ride on it and you will feel how amazing it is!

- The gerund of plan should be planning (with double 'n')
- I don't know a place called 'Canton'... Maybe you are saying about Guangdong???
- exiting???? It is incorrect spelling. Do you mean 'exciting'?
- I don't know what the Tornado is... so I do not know if it is a thing that can be rode on. So I am not able to correct that sentence. Hope you are using a correct verb!!
- I think it is better to say"how amazing it is!" rather than just "how amazing". Just my opinion.

For giving you marks... it is quite difficult because I don't know your age and nationality...
- If you are a junior primary student (P1-P3), it is really good because you can use some good adjectives which maybe quite difficult at your level. You deserve 85-90/100 i think.
- If you are a senior primary student (P4-P6), it is just fair and that is the level you should reach. However, it is a bit short. So... maybe 80/100
- If you are a secondary student, I am sorry to say that I think you are below the average. Because you have some grammatic errors and it is really too short for you. Mayber try harder to write more words and use more different kinds of sentence patterns next time. Maybe a fair pass. 50-60/100

Actually... If you can write a bit longer, it will be more easier to see what level you are at. Your composition is too short for others to identify if you are a good writter or not.

I would apologize if I have said something that is wrong or make you feel sad.
Anyway, try harder and 加油!! You are already very good because you are willing to seek help and advice from others!! You are a good learner=]
Hope I can help you!!!!