First thing I would do to try to ease your fears is to find out if you are pregnant or not. Get yourself a home pregnancy test and use the first morning urine specimen to test yourself. The first morning specimen is the most concentrated specimen of the day, so it will yield the best results. If you are not pregnant, then you can relax, but probably need to be more careful about risking getting pregnant....maybe change your form of birth control.
If you are pregant, then I would immediately stop using the acne cream and consult your doctor. The test done on this drug have shown birth defects if high (17X normal human dose) in animals. Do a web search for Tretinoin to read risk factors for pregnancy. Your dosage is so low that you are probably safe, but noone can rule out the possibility of birth defects. If you are pregnant, and concerned, your doctor may at some point want to do testing on the baby, and monitor with sonograms to make sure there are no problems.
I hope this helps ease your concerns. Good luck. Have a great day.