Hi im new to this and would appreciate some advice

I see your point.

I would also advice you to keep develop it, ideas are after all just ideas!

I have come up with something that actually has components of an existing popular game set with a new theme, some new mechanics, some new rules and as a whole a new experience. When we are playing it is really much more fun than lots of other games on the market!

It's possible to publish an expansion to an existing game, as long as you avoid using any copyrighted or trademarked material. I believe there were expansions to the original "Axis & Allies" which were not published, nor sanctioned by Milton Bradley. Of course, the trick in such a case will be to get people to know it is an expansion to that game, without using the name of the game (assuming the name is trademarked)!

Another possibility would be to create an expansion (or add-on, or whatever it is) for the game, and then try to get the original publisher to publish it. If the original game is published by a "big" publisher (ie. Hasbro), then your chances of this happening are pretty slim. Smaller publishers in the hobby market might be interested, but I wouldn't bet my money on it. Moreover, you would have to share credit and, more importantly, royalties with the original designer (example: Carcassonne - the Castle).

Finally, you could try and make a completely original game. You could base the design on another game, and then rework it enough to make it your own original design. This will require more work, but it will be less hassle to try and sell the design later on.