I'm not 'worried' about Smart's shot at all. I have never expected him to become a great shooter just a few weeks after ending his college career as a crappy one.
To be blunt, I think Smart's form is atrocious -- far worse than anyone else on the Celtics. He bends too much at the waste on his dip, causing his body to have to rock back and then forward again as he rises and pushes into his shot. As a consequence of the bend at the waste, his arms extend out too far from his body on the dip and then end up swinging back over his head on the rise. And to top it off, he tends to finish with his shoulder turned into the shot. All these things matter most on the 3PT shot where he has to really muscle it and all the flaws become amplified. He doesn't do the rocking on his set shots, so his free throws are actually decent.
Is it possible for him to fix it and become a good shooter? Sure. Anything is possible. I'm just not holding my breath. If it happens, great. It probably ain't happening soon.
All that said, I'm not worried about his shot because frankly, almost none of Smart's value as a player depends on him being a great outside shooter.
Even while shooting at a low percentage, he can still be a relatively high efficiency scorer (per FGA) by getting to the free throw line. This is where his advantage is. Not as a great outside shooter.
I would like him to start to acknowledge his limitations and just plain not bother too much with the 3PT shot. Go to the hoop. Drive & dish.