just won't compute it naturally so I'm always slow at trying to figure my trim up/down situ
Trim is either good, or less good, and as the pilot, it's really yours to decide. If you are in stable flight, and there is a control force you'd like to trim out, move the trim, until the force is trimmed out. It's only wrong, if you cannot maintain control of the aircraft.
A small factor in trimming historically was that some military types could build up immense control forces in a dive, and trimming yourself out was the only way - hence the vital need for elevator trim. GA aircraft have suitably light control forces by regulation. Just use the trim to neutralize the control forces to your liking. If you don't get it perfect the first time, you'll be just like the rest of us!
Fear not the aircraft - certified aircraft are all built to very similar standards, and they are benign. Conditions could be cause for fear (I'm certainly fearful of some conditions - so I don't fly in them). As you learn, you will be amazed at what the plane is actually capable of - look forward to learning new aspects of what the 152, or the Piper can do!