Secondary fermentation - Head Space?

I am concerned for my second brew attempt.
All was well during primary fermentation of 2 weeks on my Kolsch extract from NB.

I transferred to secondary after 2.5 weeks and am concerned that my secondary Glass Carboy has too much head room. I went from Primary of 6.5 gallon carboy holding the 5 gallons and transferred the 5 gallons to the secondary Carboy that is also 6.5 gallons still leaving 1.5 gallons of head room.

I have read, after the secondary rack of course, that this is NOT recommended as the beer can get too much oxygen, leaving bad taste in finished product. Can I mitigate any possible damage and save this brew? What should I do? Should I wait it out the remaining 3 weeks in secondary? bottle in a week? or ?

Any help is greatly appreciated.

Relax. It will be fine. The beer, after primary has co2 in it that was released after you racked and probably forced most of the oxygen out of the carboy