I think it's fine to include projects on a CV that haven't been peer reviewed with a parenthetical that they are "submitted" or "in progress", especially for early-career researchers like undergraduate students. It's a bit weird when professors with a longer CV include these projects, but I doubt many people really count it against them (and some funding agencies will consider them progress), they just will know and understand not to consider those finished published projects, because, well, they aren't.
You, however, have a preprint available for others to read, so you don't need to make any note about it being under review or anything: just include it as a preprint with all the citation information pointing to the preprint archive version of the paper. I've seen CVs that split these out into a separate section and those that mix them with other papers. If you want to be completely transparent I think a separate section is good.