Have you ever got help on the forums in a substantial way? Anyone ever go out of their way to help you? Perhaps a special thanks section. Did you not use any of the numerous free plugins provided by guys like rexrainbow, R0J0hound, linkman2004, etc? Perhaps an 'additional programming by:' section for those ones?
If you truly made your game all by yourself for however long it took and had no outside influence or help in any way then you should be proud to put your name down as the sole line of a credits page.... chances are there are more people that helped you get there than you first thought, though.
Congrats on finishing the game!