Link prediction with input data
First as "timleathart" mentioned, you need to fix your code by changing this line : 

X_test = sc.fit_transform(X_test)


to:

X_test = sc.transform(X_test)


For your question :


you have already the number of samples (training_samples) used for training. so all you need is to iterate over the y_pred and save the values in new column in the dataset starting from "training_samples" as row index.