Can excess 529 contribution be reversed within same tax year?

Yesterday I contributed $20,000 to my son’s 529, and I then remembered the $16,000 annual gift tax limit.  Since I’m still within the same tax year can I correct this to keep the contribution under the $16,000 limit.

 

Possible solution I’m thinking about:

Withdraw the $4,000 (in the same tax year).

Ask my plan provider to do a “correction” (if that’s a thing) to adjust the money transfer to $16,000 and send back $4,000 of it.

Have my domestic partner, the beneficiary’s mom, write me a check for $4,000 to reimburse me for her share of the contribution, and just call this a joint contribution from both of us.

 

Would any of those work?  Any other idea to fix this without a form 709 or doing the 5 year contribution?  Thank you.