headspace concerns

So on Thursday night I brewed up my first batch of beer. And now I think I might have a problem.

Long story short I have two 5 gallon buckets I thought were 6.5 gallon buckets. My wort was an inch away from the rim and all I had was 5/16 id tubing for a blowoff. I thought it'd be safest to split the wort into my two buckets and not risk a huge mess.

Problem is now each bucket has 2.5 gallons of headspace and from what I read that's a problem for 3 week primary.

So do I rack to a single bucket for a secondary after primary to prevent oxidation?

For primary, you're fine. The yeast is giving off CO2 and will form a blanket that protects the beer from oxygen. Secondary is much more of a concern because that barrier isn't there.

Just keep the lids on and don't open them until you're ready to bottle. Give it an extra week (4) if you want to be safe that it's ready to bottle. If you don't open them and don't overly disturb them, they'll keep their CO2 blanket inside.