Safety wise I'm worried about being lost,
Download google maps on your phone and you'll always find your way
kidnapped
Extremely rare because most people seriously don't want the hassel, You're going to big cities, there are always people awake amd on the street in big cities. Kidnappers don't want to be seen.
or ripped off by taxi drivers,
Everybody gets ripped off by taxi drivers, it's no different abroad. See it as part of the experience. Better yet, take the busses, trains and metro. Big cities have them. Every airport or hotel is connected.
air band b host being creepy,
This can be realistic, go to a professional hotel or hostel. Don't go to someones home.
falling and breaking a leg,
This can happen at home as well but if it happens abroad just remember that it happens everywhere all the time so foreign hospitals know just as well how to treat you as at home.
I'm a worrier i could think of a hundred things to go wrong
Being careful is okay, it keeps you safe. Just don't overdo it, you're one of millions of people in the city so try to enjoy your trip as well.
In my opinion, the first trip alone is the scariest, after that it gets easier. You wouldn't worry as much if it was a trip to London or Glasgow. This isn't much different, they just speak another language (but enough people can speak some english) and they might have some different and interesting foods and culture. Have fun!