Quitting job after a few days

I was contracting for an oil company and got an offer out of the blue for a full time opportunity. I prematurely switched company’s. My new company has payed me for the days of onboarding and one course. I am sick to my stomach here and fully regret my decision and want to go back to my old job. I’m trying to decide on how to break the news to my new employer if my old company allows me to go back. Ive thought about telling them they don’t have to pay me and me paying for the course they put me through while apologizing for wasting they’re time. Can anyone relate to this? I can’t stress how sick I feel and how much I regret my decision. Hoping to get some advice.

usa jobs
usa jobs resume
usa hotel jobs
usajobs
usa jobs federal government
usa job in ksa
usa jobs
usa jobs login
usa jobs gov
usajobs.gov
www.usajobs.gov
usajobs.com
usajobs
usajobs.gov official