It's impossible to say what gives. If the cut is bad, your saw definitely needs adjustment. Follow the manual to see how. With an inexpensive saw like the Ryobi, you might not ever be able to dial it in precisely and repeatably.

 

In looking at the manual it gives no instruction on adjustment. My Dewalt has a plate that can be adjusted and keep the locks in place at same time.

That being said if I am doing general construction work I am not all that concerned in a dead accurate miter. BUT for say a picture frame, yes I am. Couple of ways to accomplish this. A TS jig set up for miters where you have side a and side b cut that together equals 90 Degrees. Who cares if it is 44.5 and 45.5? OR a shooting board set up for miter cuts which can be dialed in for a precise fit.

I am sure many other ways exist, these are just two I use that work for me.

 

I had one that read 46 when it was at 45. I learned to fudge the bevel settings. I think there was a stop for 45, which I set at 46.

 

A ryobi probably doesnt have any fine tuning adjustments built in. You can probably loosen the fence and flex it a little and bolt it back down though.

 

Its not off on the miter angle, its off in plan or looking down at it. I guess I can adjust the angle of the table. Strange because a straight cut is perfect.