about the past, especially those painful memories.(note1)
I'm not clear on what you are trying to say in the last phrase. Maybe, "especially when it involves painful memories"?
no use to regret or linger in those useless past (note 2)
no point in regretting or lingering in the useless past
And I do agree with this opinion totally (note 3)
Ouch. Using "totally" to mean "completely" is very slang-y and will set people's teeth on edge. Not something you want to do for a TOEFL test. Stick with "I agree with this opinion" or "I completely agree with this position".
eternal sunshine of spotless mind (note 4)
Go over the chapter in your grammar text concerning formats for titles of movies and books.
No matter to (note 5)
This isn't an appropriate phrase, even though I know what you mean to say. For some reason, my brain is unable to offer suggestions.