I haven't watched a single episode of the most recent season for fear that it would ruin something that has yet to happen in the books. Was all my worrying for naught?
Yes, for a few things. The show really has no choice now but to keep going. They can't wait for the books any longer. Watching the show now means going past the books.
For me, personally, it doesn't matter as I am invested in the story and care not about the medium through which the story comes to me. My understanding, however, is that others do care about the medium through which the story comes to them. If you are one of them, and if your preferred medium is the books, then stay away from the show for now.
I would argue that nothing in this season goes beyond the ending of the books, with one relatively minor and honestly very predictable exception (spoiler tag contains the spoiler and the reason it is predictable).
Myrcella dies. We know this is fated from the Golden Crowns prophesy, so it's hardly a spoiler, and it seems unlikely it will occur in the same manner in any case.
However, some things happen to some characters which are not in the books. This may include going places they shouldn't, saying things they shouldn't, meeting people they shouldn't, and doing things they shouldn't (including dying). In almost all cases, these arcs and especially deaths are contradicted by book evidence, and are therefore spoiler-free.
There is one case to be made for a spoiler arc (spoiler tag contains the person/s involved only, not the events)
The Dragonstone Baratheons in the North
However, I argue that this arc is unlikely to be a spoiler, and is very probably a deviation from the books, or at the very least an incredibly abbreviated and simplified arc (as reasoned on fan blogs and the subreddit), to the point where it's basically unbelievable.