I played this for the first time today and I had the same problem and my park was tiny, only around 3 rides and 3 shops. The full business simulation was incredibly hard, even on easy, and by the time I changed to sandbox mode it was too late and I was going bankrupt.
Compared to RollerCoaster Tycoon, I was really quite disappointed. In RCT I was able to maintain a positive cashflow and gradually grow my theme parks, but here I couldn't even get chance to grow. And this was on easy too! I wonder if they simplified it for Theme Park World and Theme Park Inc?
Bullfrog games just tend to be too difficult for me for some reason. :(
Theme Park -> negative cashflow failure
Theme Hospital -> After first couple of levels it got too complicated
Dungeon Keeper -> Initial levels (tutorial and couple of levels after that) were fine, then I got swamped by the enemy keeper and ran out of gold stopping me from being able to do anything
Syndicate Wars -> First few levels, great, then not enough money to upgrade my agents
The original Syndicate, though, I got through to the final mission, though I couldn't beat that last mission. That's the best I've done in a Bullfrog game.