Hi @Cat24
I think your listing is fine how did you set.
if you have 1 or 2 guest, they get one room, if are 3 or 4 they get 2 rooms with the extra price, so till here it's work.
... but if you want 2 single guests that get 2 rooms (as friends traveller), I think that with Instant Booking it never gonna work, because the guest can book for 2 pepole and that's it.
I don't now if Airbnb during the booking process asking how many rooms the guest would like to have, (as booking.com for example) so in that case your are good, but if isn't like this you have to turn off the IB option, and deal with the guests case to case, or create the second listing.
anyway, just wait some others Host more experienced with IB.
good luck
Cheers Raf