First of all, OP, go outside and spin around three times and spit! Or throw salt over your shoulder. Or something!
Due to the above I don’t believe he would of lost many voters who backed him in that election yet he’s certainly gained more supporters since then. Therfore, unless a big majority of usual non voters are going to show up this time around and them mainly vote for Biden, I believe his chances are good.
As for this, you're not completely wrong. Trump has a low ceiling (rarely has over 43% approval) but has a super high floor (rarely polls below about 38%). Basically, those who love him love him and are unshakable, no matter what he does or says. He can insult them, and they won't leave.
Now, only about 55% of the voting age population voted in 2016. That leaves a huge margin of those who didn't vote. The numbers coming out this election cycle are insane. In many precincts, more people have voted early this year than voted at all in 2016. Which direction they're voting is less clear, but they're estimating this will have the highest turnout in over a century.
But the electoral college means that the Democrats have to win by a giant margin to win the election. Remember that Hillary won the popular vote by nearly 3 million; Donald Trump won the electoral college by about 80,000 people spread between three states. (That's basically Wembley, divided between three large states.) To get a rough sense of the effect, you usually have to subtract 3-4 points from the national average.
The key is how he's polling in swing states. Biden has a good lead in PA, MI, and WI, all of which Hillary lost. Florida is super close.
Anyway, OP, do something to break the curse!