Hello & thank you for the question. I'm glad to hear your group played Outworlder last night, that's fantastic.
Sorry for the confusion on the Fate spending. I had originally envisioned spending 1 Fate Point = +1 to any Opposition Roll (so, Checks or Combat). It's been a while since I played the game, but clearly there was a few details that I left out.
I would say you can spend as much Fate as you want in this manner (even on Fate related opposition rolls), as the movie is all about defying fate (like Rell sacrificing himself at the end). Plus, at the end of adventures you can get rewarded with more Fate points so might as well spend it here & there.
I hope this helps & sorry for the confusion on that matter. Thank you for playing!