Ok, it appears you are filling a shape with a color, not a pattern.
Your artwork is probably made up of separate paths which "appear" to create a closed shape.
You can:
- attempt to close the artwork by joining the endpoints (try selecting all and type "Cmd+J".
- or Convert your artwork to a "Live Paint" group, which would allow you to fill each area with a different color/pattern.
To convert to a "Live Paint" group:
- Select all paths of a given artwork
- Set "fill" to "none"
- Choose "Convert to Live Paint" (Object>Live Paint>Make)
- Type "K" to get the Live Paint Bucket tool and click to fill (Triple click to fill entire object with one color)
Once you get the hang of Live Paint you won't want to live without it.
BTW… there is much more to working with Live Paint objects. Research them.
Learn about the Live Paint Bucket tool and the Live Paint Selection tool. Each has it's own useful features.
Also learn about colorizing strokes in a Live Paint group. They can be colorized at the "Object" or Live Paint level, offering many useful options.