2 Missed pills in a row have failure rate nearly about 5% and it depends on timing of unprotected sex around ovulation time.
Light spotting may be due to early implantation/hormonal
etc.Do a blood test
for B-hcg/USG lower abdomen with some hormone test to rule out underlying pathology including product of conception if any.Consult with your doctor for suggestive measures.
Practice safe sex with extra protective measures like condom during ovulation time and keep taking OCP on regular basis on scheduled time to avoid unwanted pregnancy