Upvote:2
I'm assuming from your question you're a US citizen, if so you don't need to worry. You'll enter South Korea as a tourist and be granted 90 days which are ample time to leave. The immigration officer might ask you some questions, given your recent stay, to make sure you don't intend to remain there. Generally showing proof of onward travel (your ticket to the US) should be enough.
If you're from a country where a visa is required to enter South Korea, you may still be able to get in without one.
TWOV (Transit Without Visa): Holders of onward tickets transiting Seoul Incheon (ICN), for a max. transit time of 24 hours. Holders of onward tickets transiting Seoul Incheon (ICN), participating in the Transit Tourism Program for a max. transit time of 72 hours.