The problem is oxidation. You will have a huge portion of your cider exposed to air. However, if this is all you have you could purge with CO2, if you have a way to do this--like from a kegerator. If you have no choice but to do this without purging, it should turn out fine, because the co2 produced by the yeast will rise and blanket the cider, pushing up the air. Oxidation is a bigger problem post fermentation than during primary. But it would still be better to use a smaller fermenter if you can get one. Check with your LHBS. They should have some smaller containers. I've even used large growlers for small stuff and simply left a good headspace and used a blow off hose.