Which part doesn’t sound the same to you? Are you sure you’re listening to the same version as the tab you’re looking at since there’s multiple versions of this song?
The tab is just for the lead part for this song.
Is your nail on your middle finger long? If your nail is too long, it will make doing that C chord very difficult.
If not, it’s most likely just the angle of your hand. I’d recommend starting the C with just your first and third finger and once you get that sounding clear try adding your second finger without changing the position of your hand.