I bought the game for our group, then found out their plan needs a $35 expansion

At the lobby screen, my friends told me to open the expansion store page. "That's where the campaign we meant is," Sam said. I'd bought the $20 base game the previous night because he'd said, "Get this one and you can join us."

The extra $35 is more than I planned to spend. Sam offered to cover it, which was kind, but said he'd rather do that than go back to the base campaign everybody else has finished. I don't want his gift to turn every missed evening into me wasting his money.

I've played 46 minutes, mostly getting through the introduction. [Steam's standard refund offer for store games uses a two-week purchase window and less than two hours of playtime](https://store.steampowered.com/steam_refunds/). I bought directly from Steam, so I can check that route before playing more; I haven't submitted a request yet.

Would you accept the expansion as a straightforward gift, suggest a different game night, or undo the base-game purchase? I want to join them, but the invitation now has a price and an obligation I hadn't understood.