Form 3115 is not for making the election. You make the election by attaching a statement to the previous year's filed taxes. Form 3115 is used with the filings of the first year that mark-to market is used.
Example:
April 2019: When filing your 2018 taxes (by the original Apr. 15 due date) you attach a statement which includes all of the information in the original answer.
April 2020: When filing your 2019 taxes, you include form 3115 to initiate the new accounting method. (This form is only needed for the first year of mark-to-market accounting.)
