Correlative conjunctions come in pairs: either . . . or, not only . . . but also, and so on. Make sure that the grammatical structure following the second half of the pair is the same as that following the first half.
The words a prolific inventor follow not only, so a successful entrepreneur should follow but also. Repeating was creates an unbalanced effect.
To change my flight, which follows either, should be balanced with to take the train, which follows or.
Exercises:
Identifying parallel structure
Parallelism 1
Parallelism 2
Parallelism 3
Parallelism 4