we dont have test set and after prediction how will the submission file look like after modelling am having RMSE = 18 and submitting is giving me 50 on the scoreboard
"we dont have test set" : this is a forecasting competition a.k.a you will use the data in certain period to predict future values in another period. In other words, there is no test set as in classical competitions.
"and after prediction how will the submission file look like": The submission format is describe in the section Data, have a look! If you got score this means that the file you submitted is ok.
"after modelling am having RMSE = 18 and submitting is giving me 50 on the scoreboard":
1. How did you train you model ? With time series you could not randomly split your data into trainning, and test set! For example if you are using Python, don't use the function train_test_split of scikit-learn. Instead, split by period, for example the data from january to april will be your trainning set, and the remaining the test set or use the function TimeSeriesSplit of scikit-learn.
2. Check if you are not overfitting!
3. Check if your predictions index match with the submission file one.
Thanks for the insights on how to go about splitting time series data.