I've owned and given away to the kids many many prowlers. They're my go too gift rifle to start young hunters/marksman. Its an entry level rifle from crosman that use some of their more upper end nitro piston parts. At under $100 they're a great deal for a .22 that shoots 14.3g crosman domes well up to 30 yards or so.
Even with the centerpoint scope they shoot well. After I set them up right, and zero at 20 yards they all shoot a quarter size group at 750+ fps at 25 yards. Some would even get into the 800fps range. For 10-20 yards, really no reason to spend any more cash on a scope that cost as much as the rifle. Also, the cheap crosman 14.3 domes, not hollow point, have shot the best for me.
Not saying the centerpoint is a great scope,no, just that as long as its not broken or defective, it does work consistently good enough on the prowler for exactly what you're trying to do.
More than likely its not the scope, pellets, or the rifle thats giving you problems, its the way you hold the gas spring piston rifle. Experienced it myself when first starting to shoot springers, as has every kid I've taught how to shoot them. Gas spring piston rifles need an artillery hold. And until you get that hold downpat, no scope, pellet or anything will help. But once you get the right hold figured out, will be uncanny how well it shoots. Even with the center point scope, head shots at 10-20 yards will be easy and consistent... I never shot a groundhog with a prowler but can't even start to count how many (100's..?)grey nutters I've and the kids have taken, mostly all with head shots.
When zeroing in at 10 yards try resting the rifles front stock at its balance point on something solid but not something that grips the rifle not allowing it to move. A shooting stick works good, but even the top back of a chair will work. Hold the trigger/stock very lightly not preventing the rifle from moving when shot. See if the rifle performs better with this type rest/hold. See if you can zero in like that and get a good group at 10 yards. If you try and hold on tight/rigid to a prowler like a 22lr, unpredictable will not even begin to describe your frustration...
jmo