Well, there are going to be a lot more significant effects besides "France is slightly bigger."
For starters, at Waterloo alone, 47000 people were killed or injured. Preventing that is sure to have an effect on France, Prussia and Britain. Those people are going to live their lives, marry people they didn't IOTL, have children that were never born IOTL... that sort of thing eventually has an impact on history.
Besides that, culture and literature etc. will be affected. Less places named "Waterloo" for starters, and Napoleon's image/reputation will be different. The Hundred Days added to his mythos. Being defeated, and then rising back up in one last attempt... this appealed to the emerging romantic movement. (Byron considered Napoleon his idol, for instance.)
At the same time, Wellington's reputation will also be slightly different. He'll be less famous outside Britain (and the Iberian peninsula), but he was already seen as a conquering hero back home. In fact, he was one of the idols of the romantics, before he became (to them) the symbol of the reactionary forces that defeated the great Napoleon.
With Napoleon not coming back, a lot more young romantics are going to consider Wellington their hero. British romanticism might be more conservative as a result, as they try to emulate his political views...