We recommend you don't edit your options.txt file, any options should be set through the in game dialogs.
However, the options.txt file you edited, was it the one where the game was installed? If so, you've edited the wrong one, this is the file the game uses the first time you run it. Use the file search on your computer and you should find another options.txt file, it's usually somewhere like:
C:\Documents and Settings\<user name>\Application Data\Atari\RCT3
It's a good idea to save a backup as changing the option.txt can cause problems.
Michael