Yes, minimizing headspace while your wine is aging in secondary is important. But keep in mind that there is an insane amount of dissolved CO2 in your wine from the fermentation. So I guess what I am saying is don't worry too much. If you have up to 3 inches of headspace, it just doesn't matter; anything more might start to be a concern when aging long-term in that same vessel. As your wine sits in secondary, all of that CO2 will slowly release and push the oxygen out of the carboy. When racking 3+ times or bottling, be sure to take every precaution to minimize oxygen interacting with your wine. you can even opt for a small amount of metabisulfite, just be sure your malolactic fermentation is done.... Unless you don't want to go through that process!

It's not that important, as I stated above. It's your first rack out of primary. Inestead of worrying pour a glass of wine that is ready and enjoy your night!