Dobrý den,
chtěla bych poprosit o překontrolování mého domácího úkolu na angličtinu.
Děkuji, Nerevanin

Dear Diana
Thank you so much for your invitation but I'm afraid that I won't be there, though it sounds really good and I guess it's going to be a great party! I'm not able to come because two days before 14th February we (me and my family) are going at my grandmother's and we are staying there for two weeks. To be honest, I think it will a little bit boring experience but I have to come.
I'm very sorry that I haven't replied to your e-mails recently. I was very busy with school last few weeks. You know, exams and so on… I think that the last year studying wasn't as hard as it's now. But I did all these exams well, I hope so… Addition to this, I also have had to get ready for some music performances (I play the guitar and the keyboard, do you remember?).
Well, after our return back to home, we could go to the cinema sometime and then to a restaurant, what do you think about it? I heard there will be a good film, I think it's called „Married on Monday“ and it's a romantic comedy.
I guess that's all from me. Once again I'd like to thank you for the invitation and once again I'd like to say sorry that I won't be there. Please, will you tell me about everything that happened there? I'm really looking forward to it!
Love, Lucy

think that the last year OF studying wasn't as hard as it's now

3.radek od konce, mas tam 2× ONCE AGAIN, podle me zbytečně

I think that the last year studying wasn't as hard as it's now. – Tohle moc nechápu,.. Cos tim chtěla rict?

Addition to this – tohle mi přijde, jak když ja neco hledam a použiju slovnik na seznamu a vyberu zrovna to co se nehodí 

I heard there will be a good film… místo WILL není lepší WOULD? (reported speech)

are going at my grandmother's and we are staying there for two weeks. ta předložka AT se mi nezdá

Určo by se tam jeste neco naslo

To be honest, I think it will a little bit boring experience – nějak mi tam chybí sloveso
after out return back to home – nevím, jestli tam nemá být back home (místo back to home)

děkuji moc Velmi si Vaší pomoci vážím

(I and my family) – častá chyba aj u samotných native speakerov, ale KTO? – JA = I
going to my grandmother`s
I did well at all my exams
In addition alebo Besides
after our return back home
I heard there would be a good film

Ještě jestli můžu, sloveso return = come back…tzn. podst. jm. return = „coming back“, nebo jak to mam napsat…čili vynechat BACK

me and my family → „my family and I“