Can I be pregnant if one drop of sperm fly away from the ejaculation and came on my vagina lips on 13/8 knowing that I am virgin. Last period on 25/8?

No. Sounds like you had your period a full 12 days AFTER the encounter - correct? So no, in your case you're not pregnant. But yes, technically one drop can do it. Plenty of stories of 'virgins' getting pregnant without any real intercourse.