What is the best course of action for a 23-year-old man, religious, respectful, and working in a government sector, after his marriage proposal to a girl of similar age who is studying at university was rejected?

What has befallen you was not going to miss you, and what has missed you was not going to befall you. Everything is by divine decree and preordainment. If you cannot convince the girl to marry you, then look for another among those of piety and good character, and forget this girl. Your marriage to her while she is unwilling may end in failure.