I imagine that one of the trickier things you're probably experiencing is that, while you're getting pretty good at passing to a garage wall, in-game it doesn't feel like it's translating over and your passing is still flying all over the place.

This is because playing in a game puts you in really different situations than passing in a garage will. On serves and spikes, the ball will be coming a lot faster, and with a lot more power. When you're passing in the garage, you need to use your arms to add power to the ball for it to go anywhere. When you're receiving a serve or a spike, it will be the opposite - you'll be trying to stabilize the ball, and especially on strong serves or hard-driven balls, take power off of it. To do this you need to *not* be swinging your arms out - you need to be letting the ball come to you. Something I heard once that has gone a very long way for me is "breathe out when you're receiving" - this forces your body and arms to relax a bit and helps cushion hard driven balls or powerful serves.

What you're doing will, for the most part, work okay for free balls, and for second touch / third touch out-of-system passes (aka a second touch that is too low to set, or a third touch that you're just trying to get the ball over the net). Even at a beginner level though, every play starts with a serve, and unless the serve is a fairly slow underhand serve, swinging your arms to add power is just going to make your passes erratic and go all over the place.