Yes, you should be concerned. If You were me (Or if I were you and you had a kegging setup) I'd purge the excess air out of the vessel to keep the O2 at a minimum.
You could also buy a bunch of marbles, or some other easily sanitized objects, and add enough of them to bring the level of the hooch (sorry) up close to the neck. Just make sure they are food safe and easily cleaned again afterwards.
Another option is to just use a large plastic bag of some sort and place it in a bucket and squeeze the excess air out. I have some bucket liners that I sometimes use for fermenting beer or wine in that makes cleanup a snap.
Since you are listing your volumes in litres, I'm assuming you are not in the US or Canada, so I'm not sure how easily it would be for you to find these things in your God-forsaken area of the globe.