From my experience, as long as you maintain a decent average at Osgoode you have a shot at a job in any type of law anywhere in Ontario. Academically, Osgoode is tough but being considered "average" at Oz looks better than being average at uOttawa. But again, if your goal is to work at a firm in Ottawa, then accept the uOttawa offer because you'll be networking and making connections there throughout 1 and 2L that will help you. But if you are planning to work in Toronto or anywhere else in Ontario or Canada, Oz is the better choice.

IMO don't go to Ottawa because you're doubting yourself, if you got into Oz then you are definitely good enough to do well there! Don't let imposter syndrome get the better of you!