Unprotected sex by withdrawal method has failure rate near about 14%. Precum or prostatic fluid (released before ejaculation) contains small amount sperm and causes pregnancy
in some percentage. Though it depends on fertile days.
Pink spotting may indicate implantation
bleeding. To confirm, you need to undergo one blood test
& TVS scan around 4-5 weeks (from LMP) for accurate result.
Following test report, consult with your gynecologist for next line management. Good luck.