Besides the literal meaning, is this sentence also used as a courtesy reply (something like "don't mention it" in English)?
I know this is so late, but I was wondering about this myself recently. Native speakers can probably tell us better, but from what I have been able to find, the equivalent of the English pleasantry "think nothing of it" could be Det var inget or det var så lite; I've also heard Ingen fara and Ingen orsak (respectively, no danger and no reason, which sound a little more casual to me), and det är lugnt- that seems to be more for when someone apologises to you, rather than thanks you.
There's an annoying bug that makes this kind of thing happen sometimes. Contractions should always be accepted automatically and the machine tells me Don't think about it is an accepted answer.
So sorry but the bug seems to be more general than that – sometimes accepted answers aren't accepted, it doesn't seem to be tied to contractions specifically. It's the annoying kind of bug that doesn't occur regularly or in specific situations, but seemingly randomly which makes it all the harder to fix I guess.
Oddly enough, this is one of the very few examples where I could imagine myself saying on, as in "Don't think on it" to specifically mean not to muse or reflect on something. Duo doesn't accept that answer, and probably shouldn't, because it's definitely non-standard, but it popped into my head.
I remember now: it's a Hagrid line from one of the Harry Potter films (and shows up high in the google search, which just reinforces that it's not a common phrasing).
I think it is a pretty common phrasing, but maybe an informal one. Personally, I would say it but not write it.
Is there an audible distinction between "Tänk inte på det" and "Tänk inte på dig"?
It's easy to remember what chirelchirel wrote by thinking about the other (I think actually more common nowadays) way of spelling dig: dej.
In theory, the imperative in English is always accompanied by an exclamation mark (!). Is this not the case in Swedish, I wonder?
In principle there should be an exclamation mark here in Swedish too. I don't think there's any big difference in how those are used generally between Swedish and English.
For some reason Im getting this sentence an absurd amount of times in this lesson,literally three in a row and still showed up later.I suppose its a bug,right?