That happened to me the first time I created my own park in the editor. I never noticed it until after I had my main paths shops and scenery built. I opened the park, and the guests just circled on the edge of the page. I couldn't edit it, so I just went ahead and started a new park. And, saved the new park over the one I screwed up.
Now I have several of my own parks. But, my favorite thing to do is the build your own Magic mountain scenario. I have several Magic Mountain parks.
My biggest Magic moutain has 32 rollercoasters, The longest coaster is the Beast, which I built when I removed the mine ride, It's over 9,000 feet long, has 6 underground tunnels and has a beast-like double drop over the loggers run. There are currently over 5,000 guests in the park, and I have over $1,000,000 in cash to spend on improvements.
My second biggest Magic Mountain park has 28 coasters, Inluding a replica of Shivering Timbers that I built back behind the psyclone and the go-carts. I also have an awesome inverted coaster in that park that has 4 underground tunnels called Insanity. It has 8 inversions, and is at it's top speed during the middle of the ride, as I built in into the side of a hill.
I also have a MForce-like coaster called Maximum Force over by the Viper, wich is close to 10,000 feet long, and has a 250 drop at 85 miles an hour.
I love rollercoaster tycoon.