The yellow coloured substance on your skin was a scab, as the sunburn
you described appears to be 2nd degree superficial burn. These burns usually heal spontaneously without much scarring.The care you should take in this case is to keep the face clean by washing with tap water and applying an antibiotic cream like Neosporin
, 2 to 3 times a day.
Dr. Anubhav Gupta