So long as it was booked through BAEC (and not Avios.com) then being Gold allows you to change things without a fee.

If you have more than 24 hours before the return journey you can still amend that booking (and hopefully it will work online too) to make it to another time. I believe you can also make it a single at this stage and thus get a refund on Avios and fees, but I would guess that needs a telephone call.

Not only can you have Avios as single trips but I would very much advise you to always book singles, particularly with Reward Flight Savers. It costs the same and gives you more online flexibility. The only exception is that most redemptions to the US cost more if done as 2 singles due to differences in the carrier charges, but to other destinations it should be about the same or sometimes even a bit cheaper.