Not at all worried about Sallis's 3PT shooting.
First, 43 attempts is an EXTREMELY small sample. Like, comically low. He also took a grand total of 19 3PT attempts his entire freshman year. For comparison, Tyree took 214 3PT attempts last season alone.
Second, FT% is widely accepted as a very strong indicator of a player's shooting potential. Sallis's was 78%, which is outstanding for a sophomore* with limited attempts. It also tends to indicate he doesn't have the "jitters" or anything, since it's not easy to consistently make FTs when you don't take all that many in the first place.
Third, as a failed former HS basketball player, I will just note how difficult it is to shoot a consistent 3PT% where you come into the game unsure how many three point attempts you might get, or whether you will get any at all. Sallis's game log shows A LOT of 0-1s and 0-0s. Really really hard to shoot a high 3PT% when you're not sure if your next shot will be your last. This kid is going to rake once he's consistently working up a sweat without being worried he might get yanked if he misses his first attempt.
* Edited to note that Sallis was actually a sophomore last year, not a freshman.