Can someone help me find the mistakes in the following sentences?

Question

The sentences are short but I want to be sure about the correct use of the prepositions.
Thanks
1. I went skiing with my dad to St Moritz (OR in St Moritz)
2. At Christmas (or On Christmas Day) I ate a lot of sweets
3. I chatted with my friends ON my computer
4. I helped my mum with the housework, for example (?) I cleaned the table and I tidied my bedroom.
5. I played songs with my guitar, which I found ON the web (?)
6. I helped my grandparents with the animals (OR I helped look after my grandparents’ animals?)
7. My Christmas holidays are just finished (OR have just finished)
8. They lasted a week but I feel they flew (??) OR they have just flown by
9. I also spent two days in the mountains with some of my friends (or some friends of mine??)
10. I like the snow very much and I enjoyed skiing a lot (?) and throwing snowballs
11. On Christmas Eve I went to a church to see one of my friends who acted in a performance and after that I stayed for the midnight mass (OR I attended the midnight mass)
12. After the mass I went back home and I exchanged presents with my friends.
13. The most exciting moment was the Christmas Day when I got up early to unwrap the presents that were under the Christmas tree.
14. During my holiday (or holidays?) I went to… I returned home for Christmas, because I wanted to spend it with my family.
15. I spent New Year’s Day with my friends at Paul’s home (OR house?)
16. My holiday finished on……(holiday or holidays?)
17. My uncle prepared a good fish (can you say that?)
18. We exploded or we burst a lot of crackers (?)
19. In the evening I watched TV up to late (or TILL late?) Can you say I usually stayed up late watching TV.
20. I made a lot of Christmas presents but I received a lot , too.
21. On my Christmas holidays (or During ….) I got up late.

Answer 1

Franco,

Please go over these aloud, and then post the ten (no more than ten) that you absolutely have no clue about.

Answer 2

1. in
2. During
6. either
7. have just
8. have just flown
9. either
11. either
13. Christmas Day = drop "the"
14. holidays is a bit better
17. yes
19. till late or the last
20. During

Sra