Many thanks for taking a look.
In the middle of the flint there is a curved swirl of white which ends (on the left as you look at the flint) in what looks like a head with an eye and mouth. The white swirl is raised from the flint. I guess it must be a mineral swirl of some kind, rather than a fossilzed fish.
I'm afraid the marks you're seeing are just the variation in the surface of the flint. Flint weathers to different colours once exposed, which often picks out scratches or slight impurities in different colours like this.
When you say that it looks like a head with eyes and mouth, you have to bare in mind that fossils are (with rare exceptions fossilised in unusual conditions) the remains of the hard parts of organisms such as the bones or shells, as soft parts are fragile and are destroyed before they can become fossils so when looking for fossils that you are looking for fossilised bones etc and not a resemblance to the overall shape of an animal including soft parts when it was alive. Soft parts are only preserved in very rare circumstances and would not look like this or be in flint. The best way to get a sense of what fossils look like is by looking at them in a museum or online if this is not possible.
One name for such coincidental resemblences is pseudofossils and they are very common enquiries. You can find more examples of pseudofossils on my blog: http://www.nhm.ac.uk/natureplus/community/identification/blog/2011/05/24/im-afraid-its-not-a-fossil-my-favourite-pseudofossil-ids
If this has sparked your interest, then the best way to get a sense of what fossils look like is by looking at lots of them in a museum or online if this is not possible.
Flint is an interesting rock that often throws up these fossil look-alikes to catch us out. Real fossils can be found in flint. I've attached an info sheet about it. You can see some flint fossils on www.discoveringfossils.co.uk
Better luck next time!