I forgot to include the following statements. Thank you very much for your help.

1.On the seventh of January my holidays were finished (or finished, had finishes) and I went back to school.
2.On New Year’s Eve I was invited to a party at a friend’s house.
3.At midnight of Christmas Eve I went to church with my family for the Christmas mass.
4. I went snowboarding to St Moritz (in ?) Can I order the side order (dish?) later?
5. I spent all my afternoon (or the whole afternoon) chatting with my friends.
6. I helped my mum prepare the lunch.
7.I went to the midnight mass where I exchanged presents with my friends.
8. I opened my gifts or my presents?
9.We went to the restaurant for lunch or we had lunch at the restaurant.
10.Can you say “butter and sage ravioli” or is better ravioli with butter and sage?
11. My relatives arrived (?) to spend Christmas Day with us.
12. She had a baby during the holiday (or during her Christmas holidays?)
13. For my starter I'll have a soup of the day and for my dessert a home-baked bluberry pie.
14. He was very impolite (rude). He poured the milk shake over (on) Jason.

1.On the seventh of January, my holidays were finished (or finished, had finishes) and I went back to school.

I would change this to: On the seventh of January, my holidays were over, and I went back to school.(You could say my holidays were finished, or had finished, but it depends on what tense you're using.)

4. I went snowboarding to St Moritz (in ?) Can I order the side order (dish?) later?

(Generally people say I went snowboarding "at") Can I order the side dish later?

5. I spent all my afternoon (or the whole afternoon) chatting with my friends. (You can use anyone. I would use the afternoon)

8.They're both the same thing, so it doesn't matter.

9.Both are fine.

10.ravioli with butter and sage

11.My relatives arrived (?) to spend Christmas Day with us.

(You could say My relatives came over to spend Christmas with us.)

12. During the Chrismtas holidays.

13.For my starter I'll have soup of the day and for my dessert, a home-baked blueberry pie.

14.He was very impolite (rude). He poured the milk shake over (on) Jason.

You could say impolite or rude. I'd use impolite. He poured the milk shake all over Jason OR on Jason.

For number 4, I guess you say "in"

No problem! Here are the corrected statements:

1. On the seventh of January, my holidays ended and I went back to school.
To correct this sentence, you can remove the phrase "had finishes" and replace it with "ended," as it is the past tense of "end."

2. On New Year's Eve, I was invited to a party at a friend's house.

3. On Christmas Eve, I went to church with my family for the Christmas mass at midnight.

4. I went snowboarding in St. Moritz. Can I order the side dish later?

5. I spent the whole afternoon chatting with my friends.

6. I helped my mom prepare lunch.

7. I went to the midnight mass where I exchanged presents with my friends.

8. I opened my presents.

9. We went to the restaurant for lunch.

10. Can you say "butter and sage ravioli," or is it better to say "ravioli with butter and sage"?

11. My relatives arrived to spend Christmas Day with us.

12. She had a baby during the holiday.

13. For my starter, I'll have the soup of the day, and for dessert, a home-baked blueberry pie.

14. He was very impolite (or rude). He poured the milkshake on Jason.

Feel free to let me know if you need further clarification on any of the statements!