Squeeeeee!! So much love for this! It absolutely glows!! And sure, this movie was uber popular in America, at least when I was little. (When I was four I was head over heels for the butterfly, who in English sings part of "Has anybody here seen Kelly, K-E-double L-Y..." ...which is my name, so I felt special).
Also I heard a rumor they were gonna making a live-action version of Last Unicorn, and I think using some of the (English) voice actors as live actors... only in older parts. Like, Mia Farrow as Molly Grue, etc (but still Christopher Lee as Haggard!). I even saw an official webpage for it once, but that was something like 4 years ago. Maybe they abandoned the idea. Cry.
But your picture is absolutely stunnning, and I can't believe you did that on the inside of a card! Beautiful!