Try not to be upset when your mind wanders, going "ah crap I really suck at focusing, now back to SSILD". When your mind wanders it means you're closer to falling asleep, so acknowledge that and drift back into the SSILD cycles. With SSILD, you are supposed to actually fall unconscious so don't put any effort into staying alert, just enough effort to get it in your mind to keep performing SSILD.

Edit: just realized you're the person I've been PMing lol. You got this I know it, never give up never surrender.