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I'm a German citizen. I was on vacation in Tijuana and I entered the US an the San Ysidro border control. I got the green I94-W form. I did some day trips to San Diego and back to Tijuana, but I completely forgot to return the I94-W form after my last visit to the US.
I flew back to Germany from Tijuana airport after a stay of 3 weeks. I still have the boarding passes of my return flight, but no further stamps in my passport. I'm planning to go to Tijuana again, but I'd like to arrive in San Diego and then go to Tijuana from there, because it's much cheaper.
Am I going to have a problem entering the US? Is it enough of a proof that I left the US in time if I show the boarding pass from my return flight to Germany departing from Tijuana airport?
The CBP help page says "If you departed by a commercial air or sea carrier (airlines or cruise ships), your departure from the U.S. can be independently verified, and it is not necessary to take any further action", but I didn't depart from the US. I'm kind of clueless now and would appreciate some help.
Thanks for your help!