Fluorine is more electronegative than nitrogen. The best explanation is that :

the nitrogen has half filled valence shell electron c.onfiguration, ${\mathrm{ns}}^2 {\mathrm{np}}^3$ where as fluorine has partially filled electron configuration  $n{s}^{2}n{p}^5$ .

the electronegativity decreases from top to bottom in each of the group as the effective nuclear charge remains constant.

the charge on a F nucleus Is +9, while that on N nucleus is +7

the valency electrons in F are on average, a little farther to the nucleus than in N