I don't have enough context to understand this sentence. Is it a slang of US people ?
I may be wrong, but I highly doubt it. I'm Jackson
I may be wrong, but I highly doubt it. I'm a Jackson.
And here "Jackson" is a surname, which can be replaced by any surname: be it Smith, Jones, Futgvuff, Stroganoff,...
It is a meme, which stems from the politically-opinionated book of former basketball star Charles Barkley entitled I may be wrong but I doubt it.
Now its just a way of showing off your surname on t-shirt or sweatshirt.
Alternatively, in
I may be wrong, but I highly doubt it. I'm Jackson.
Jackson could be a first name (example: Jackson Brown). The same meaning applies, whether the phrase is a Jackson or just Jackson.
The first part:
I may be wrong, but I highly doubt it
is then supported by the phrase
I'm Jackson.
Which means (according to the Urban Dictionary):
A guy that's like crazy perfect. He's tall and strong and ...Overall, Jacksons are the best thing in the world...
It's a brag that has become enough of a catchphrase that merchandisers have picked it up for display on t-shirts and hoodies.
It means exactly what it says: "I concede that it is possible (in any given context) that I could be wrong, but that possibility is small." In other words, if we're arguing about something "I'm right".