Hi Quoc
Your sentence structure is fine.
I'm not sure what you mean by "report" it. Your sentences would be the direct speech used to talk about the letter you want(ed) to write on Saturday:
On Friday (yesterday) you decided to try to write a letter on Saturday. So, on Friday your direct speech was: "Tomorrow, if I have enough time, I will write to my parents."
On Saturday (today) you say: "If I had enough time now, I would write to my parents." (This if-sentence tells me that you want to write the letter now, but don't have time.)
On Sunday (tomorrow) you might talk about how you didn't write the letter on Saturday: "Yesterday, if I had had enough time, I would have written to my parents."