Hey guys
I've learning how to play Dammit by Blink 182 and it's simple enough tabs and a easy song but there is a problem that I am facing. The palm muting I do doesn't really sound anything like theirs.
That's the instrumental version of the song and the palm muting I'm talking about is at about 20 seconds in, has anyone got any tips for me to make it sound like that?

My Gear is a Line 6 spider 4 15 watt amp
Boss Me 70
For what you're talking about, I believe you have do all the palm mutes by playing them straight down, instead of alternating up and down. It's tough to do at first cause you have to play pretty fast, but stick to it and you'll get it.
We can't really know what causes the difference between your sound and their sound if we can only hear them. Try recording yourself and sharing with us.

He's a piece of advice regarding technique that might get you closer to what you want:

Try experiment resting your muting palm in different places between the bridge and the neck. Usually, the farther away you are from the bridge and towards the neck the more muted the note will be.
Costantly pick the string(\s) while slowly moving along them to experiment.
"Yeees I am your god!" John Petrucci, Phsyco excercises
With this song, I use down/up Palm muting. I would try just playing it really quickly. remember the first strum on each chord is played without palm mutes the first time, then it's followed by quick and heavy down up palm muting.
When palm muting power chords play the 2 notes, and down pick. When not palm muting power chords play the 3 note power chord (power chord+octave) and do up/down strokes