Simple 8621 questions

[CdnAmerican]

I am a USC in Canada. I held a mutual fund in my RESP because I planned badly. I have used mark-to-market on the 8621 form every year since I have held this fund. I finally sold it during 2018.

a) Do I need to file an 8621 for it for 2018?
b) Do I claim this as a capital gain (loss), based on my fair market value as of the end of 2017?
c) If it's a loss, can I carry that loss over?

Thanks in advance!

[CdnAmerican]

A little further info … I guess I'm still unclear after reading the instructions for the form; I am not sure if the form is required if I held the fund at any time during the year, or if it's only needed if it's owned at the end of the year. I found some other posts (MGeorge) that were close to this, but none that specifically addressed it ..