Does it use .22 (5.5mm) pellets or 5mm (.19/.20) pellets? I actually wanted one of those I saw locally, but ended up realizing it was in fucking 5mm and none of the stores I go to sell them. Not to mention, I don't even know if the most common companies (Daisy, Gamo, Crosman) even make 5mm in the pellets I like. Pretty air rifle, though. Just wish it were in something I could find. Seems pretty reasonable to hunt squirrels with; according to an article, they have about 13 foot pounds of power.
Also, as for your squirrel, I've noticed that they often simply run up to the top of the tree at the end of a branch somewhere. Often, they go back to finding acorns like nothing happened, waiting for you to leave (or forgetting it ever happened?). As stupid of a method as this sounds, it can be useful to have a cheap 10 pump filled with BBs for cases like this where you lose squirrels. Once you're sure you lost sight of it and it has no other trees to jump to, keep an eye on the tree, load a BB, pump it to maybe 5, make sure you have a safe shot to take into the tree, hopefully hitting it off the trunk or a branch, bouncing it upward through the tree, so none of the energy is in the BB once it comes down. The BB being shot through the tree & striking nearby leaves will make the squirrel think you took another shot at it. Sometimes, the shot isn't close enough and it doesn't react or is trying to hide so it doesn't react until you get much closer than normal. Once you shoot into the tree, it will often run to the opposite side, so keep an eye on movement while you switch back to your other pellet gun, then look for leaves shaking as they often go back to messing around at the end of a branch. Move to a spot you can see the squirrel, then either headshot it (if you have no adrenaline shakes) or shoot it in the heart/lungs. Heart/lungs aren't my thing, but I've realized adrenaline wrecks groups and heart shot is quick. Also, 880 is useful for this because it's quiet.