Check this by holding a level against the bottom edge.
How to tell if fascia board is level for gutters.
Snap a chalk line to indicate the top of the gutter.
Press the board tightly against the ends of the rafters so the top edge is level with the tops of the rafters.
A loose gutter system can also damage your boards as it pulls away from the wood.
If your fascia boards are level you can use them as a reference for sloping the gutters.
Gutters should have a small amount of fall toward the downspout or be level at the very least.
First consider leafguard gutters or a similar covered gutter system that will prevent clogs and splashing.
Thankfully there are ways to counter this damage.
Also make sure your gutter piping is firmly attached to your fascia board.
If they aren t level adjust the string line until a level aligned with it shows a slight slope.