Shapes Question

I was doing a question which says:
Explain why BCl3 has a trigonal planar shape with bond angles of
120°.
In my answer, I talked about how the central boron atom has three bonding pairs of electrons, and that the 3 bonding pairs of electrons repel each other equally, causing BCl3 to take up the trigonal planar shape to maximise separation and minimise repulsion.
However, I effectively got 0 marks on this question because the mark scheme states: "Do not award 3 bonding pairs repel each other equally".
Would anyone know why?