Checking the photo of a trackpad for the MacBook, I have noticed there's 2 mounting pads in the lower edge of it. And now I remember when I reached my trackpad, these 2 mounting pads were missing. I think this is the reason why it's not flush with the body of the MacBook.
Regarding to the loose screws, when I open my MacBook again I'll double check to see if one of these screws are missing in the parts you mentioned in your answer.
Thank you very much Jeff.