I would recommend you read Linus Pauling’s Nature of the Chemical Bond, an excellent book for VBT.
Basically, the reason for hybridisation is to increase bond strength, which is maximised at 2 when one has 25% s and 75% p character.
However, having a lone pair in an s orbital is more stable than having it in a hybridised orbital (due to promotion energy), so in cases with lone pairs we end up with the lone pairs having more s character and the bonding pairs having more p character. This is the same for any compound with lone pairs.
Case in point- the lone pairs in water have 44% s character, while the bonding pairs have 6% each.
To answer your question, nitrogen is much more electronegative than hydrogen, so the interaction is somewhat ionic. Hence, the bond angle increases just like in water- the predicted bond angle for water would be about 90 degrees, but that is obviously not the case.
At the end of the day, VBT is much more complex than one might think if one learns it in organic chemistry.