Is my sentence 如果没时间的话就告诉我 grammatically correct? I am not sure that my sentence: 


  如果没时间的话就告诉我 


is grammatically  correct or not. So please guide me, have I used the right words?
如果没时间的话就告诉我 


Your sentence is grammatically correct and it is a very common grammar structure

[如果 X 就 Y] = [If X then Y]

[1: 如果] [X: 没时间的话] [2:就] [Y:告诉我] 

[1: if ] [X: suppose you have no time] [2: then ] [Y: tell me] 

Notice 1: The subject 'you' is omitted in Chinese sentence and it is a very common practice, you can drop the subject as long as it is clearly understood in the context. 

Notice 2: Since [如果 ~ 就] is a common structure, you can omit 如果 and write "(如果)没时间的话就告诉我". The sentence would still be correct because "如果" is strongly implied with the present of "就"

Notice 3:"的话" in "没时间的话" means "suppose" . And you can drop it too. The result is a blunter sentence "如果没时间就告诉我" (if you have no time, then tell me) sounds more like a command  than a suggestion or request