I accidentally deleted part of a video on my iPhone?

I was trying to trim it and ended up saving the part I wanted to trim and deleting the part I wanted to keep. Instead of selecting to save it as another clip, I chose "trim original". I know it's probably not possible, but I just wondered if there's any way to undo what I did and restore it back to the original length?

Not unless you have it backed up to a cloud, which hasn't synced since before you trimmed it. I'm so sorry, I understand how bad this can feel.

Unless you some how saved it to your cloud it is not recoverable

You may refer to this guide, it provides 3 ways to recover iPhone data like videos, songs, photos, contacts, notes, email, message, apps and documents. Hope it helps you.
http://www.mac-dvd.com/3-ways-to-recover-iphone-data.html