I'm not an expert on HPL's handwriting and the images aren't great, but it sure looks like his, and the "The End. Thank gawd." is very HPLish.
A remarkable discovery - I hope it winds up someplace where it is published. This presumably is the article on astrology that HPL (and CM Eddy?) ghostwrote for Houdini's planned(?) _The Cancer of Superstition_. According to Joshi, "This article has not come to light; but perhaps it supplied the nucleus for what was apparently to be a full-length polemic against superstitions of all sorts." HPL was paid $75 for the article on astrology.