Assuming your arrows are straight and if you are RH and the arrow is clearing the sight window cleanly (not bouncing off the sideplate), your arrow is likely too stiffly spined. I'm a lefty so everything is backwards for me.
However, eye-balling flight a very coarse way of checking tune. Some can eyeball very well to at least get close. Often times the "Well Behind the Archer" coaching position(10-15 feet behind) is useful in watching arrow flight. This helps the observer see around the shooter.
Lots of great threads here about tuning with paper, broadheads, bare shaft, etc.
A quick check could be helpful if you can put on a lighter field point to stiffen the dynamic spine of the arrow.
Dave is right below. I had "too light" before editing. I double-checked and Damascus Dave got it. Sorry, I'd rather be wrong than confuse you.