You need to amend. The reasons for filing an amend instead of 3115 are:

• You claimed the incorrect amount because of a mathematical error made in any year.
• You claimed the incorrect amount because of a posting error made in any year.
• You claimed the incorrect amount on property placed in service by you in tax years ending before the statute of limitations has expired.
• You are changing the amount of Section 179 claimed or not claimed.
• Election to apply the $2,500/$5,000 de minimis safe harbor rules.