Seeing as date and meeting are both feminine, shouldn't the last bit be "Dis la moi"?
le is not replacing réunion or date, but the whole clause (si tu fixes une date...) and in that case we use the masculine in french.
Why is it "tell me" and not "tell it to me". Wouldn't "dis-moi" be correct for "tell me"
tell it to me!
if you fix a date - literal, but why not correct?
'Fix a date' is accepted.
fix a date not accepted and nor tell it to me both of which are literally correct. reported
Pourquoi pas dis-la-moi?
See above. This question has already been answered.
Tell me it not accepted