I wouldn't sweat it too much. Yes, it is too much headspace, but I think most of us have been in a similar situation before and had the beer turn out fine.
Since you moved it to the secondary after only 2 weeks, I am guessing that the fermentation might not be completely 100% finished, combined with the stirring up of the yeast, I would bet that you have created a small blanket of CO2 that is protecting the beer in the secondary. CO2 is heavier than air and it will protect the beer from oxygen, which is what you are trying to avoid (oxidation).
If you have any CO2 at your disposal or maybe some argon (like a spray can for wine bottles), you could shoot a little of it in there just in case, but I bet it will turn out fine, regardless.
On another note, you made no mention of gravity readings. FYI, you are not supposed to move the beer from the primary to secondary until you are at final gravity, which can only be determined from a gravity (hydrometer) reading.