Go to a campsite that's well populated if you can't bear being out in the wilderness. If you really are that chicken about it and more worried about humans than animals, then buy a tiny padlock. You can thread it through the two zip fasteners of the tent doors once you're all zipped up and settling in for the night.
Of course, you'll just have to hope you don't a) lose the key and b) need to pee and fiddle with that to get out during the night.
Bears I hear don't know how to work a zip. That may or may not be true.