It's completely normal to have a flashback if you get high long after the trip is over. Mentally, it's still the same high for me, but I'll get some very minor visuals for the first half-hour or so. I noticed the first time getting high in months after a shroom trip that I got horribly paranoid, although I think that's more of getting used to bud high again than any shroom usage. It'll go away the more times you get high after the trip, at least it did for me. Occasionally, I'll still get visuals but that's more rare now.
It's nothing to worry about, and there's nothing you can do to make it go away. Better to just enjoy the fractal mini-light show.