> Tomorrow my school carnival. So I really excited.  My school carnival will show some dancing and singing. I’will tell you for next class. And I’will wear pretty clothes. I really excited for tomorrow's school carnival.

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*Correction :     Student'ssentence        Correctedsentence        Grammar explanation     Better sentence    

Tomorrow my school carnival.

Tomorrow is my school carnival.

Use the -be verb IS to indicate your singular subject, which is "school carnival".

So I really excited.

So, I'm really excited.

Place a comma (,) after SO if it's at the beginning of a sentence.

Use AM to link your subject and adjective "excited". I+am = AM is used with the subject I.

My school carnival will show some dancing and singing.

This sentence is correct.

I’will tell you for next class.

I will tell you next class.

The apostrophe (') is not needed between "I" and "will" unless you're using the contraction "I'll".

Either "Next class" or "on the next class" is correct.

And I’will wear pretty clothes.

I will wear pretty clothes.

The apostrophe (') is not needed between "I" and "will" unless you're using the contraction "I'll".

I really excited for tomorrow's school carnival.

I am really excited for tomorrow's school carnival.

Use AM to link your subject and adjective "excited". I+am = AM is used with the subject I.