Two girls, note, fit together perfectly (10)
I believe the answer is:
tessellate
'fit together perfectly' is the definition.
I can't judge whether this definition defines the answer.
'two girls note' is the wordplay.
'two girls' becomes 'tessella' (I can't justify this - if you can you should believe this answer much more).
'note' becomes 'te' (musical note).
'tessella'+'te'='TESSELLATE'
Can you help me to learn more?
(Other definitions for tessellate that I've seen before include "marked in little squarish areas" , "make a patterned floor?" , "Form a mosaic - sell estate (anag)" , "Create mosaic" , "Decorate with mosaics" .)