4 months is awesome! Congratulations!
And I love your idea for a tattoo: The Weasley twins would be so proud! It's cool that it was the spell that closed the marauders map (if I remember my HP right). I like the symbolism of closing a map, especially one like the maruaders map. Great idea.
I have a tattoo planned for 1 year: My last one (I've accumulated quite a canvas over the years): An open book with blank pages.