Let's start with 'welcome to the site'. My thoughts are that you didn't find a true arrowhead in the sense that the artifact pictured never actually tipped an arrow (some 90% of what people call arrowheads are actually knifes or spear points or dart points or something like that). But I believe you definitely have a prehistoric artifact. Could be a chopper, a scraper, a rough knife, a preform, something like that. If that's your first find you're doing just fine. There are generally more than one to be found, so I'd suggest heading back to the area and keep hunting for more.
Joe