Yes! I went to science fair before!
It was about the earth and the galaxy!
There was many things to see!
It also taught me about terrestrial planets, and Jupiter planets!
I think it was a great experience!

"Let your words always be gracious." ​—Colossians 4:6

=

Yes! I went to the science fair before!
It was about the Earth and the galaxy!
There were many things to see!
It also taught me about terrestrial planets and Jupiter!
I think it was a great experience!
= We usually use "the" when referring to a specific event such as a science fair.
= When referring to our planet, Earth is a proper noun and should be capitalized.
= "Many things" is plural, so it requires the plural verb "were", not "was."
= A comma is not needed before "and" when connecting only two items. Also, "Jupiter planets" is not a standard term. The revision simplifies the phrase, though a more accurate scientific term would be "gas giants" or "Jovian planets."
= Good job!