Denford Software & Machines

Here is a photo of something that I had bobcad make a code for. It has lines cut into it that aren't supposed to be there. I'm using a flat end mill. Should I use more or less stepover distance. The bit is 3/16.

it's part of this

It's hard to see from the photo - I take it the shape is curved ?
That type of design would probably come out better with a ballnose cutter - a flat cutter will leave lines on curved surfaces as there is only a small part of the tool diameter in contact when machining a slope.
Increasing stepover would improve it but I'd try using a ballnose for the finishing (use a larger flat bottom cutter for roughing if required)