Magazines can be finicky in general...even more so when you get into cheaper and cheaper handguns--materials used and fitting process really takes a dive when they try and build a "budget" pistol.
I've hand brand new $30-40 magazines that have needed slight tweaking from the factory. New doesn't always mean perfect--magazines are no different than new automobiles, computers, or even fast food. Sometime you just don't get what you were expecting.
Hi-Point has great customer service...send it back, or have 'em exchange the magazine and see if that helps. MIght be a good idea to buy a few more magazines. A semi-auto with less than 3 magazines is a waste IMHO. From what I recall, hi-point is the cheapest place to get mags.
Don't feel bad about spending $140.
It's nearly impossible to find 'em less than that in my area. I often see 'em marked $150-169 at gun shows, though they will haggle a bit.