You have 4 options:
1. By SPORTFUL BUS: organization book a coach with bike trailer up to 35 passengers.
WARNING: BUS TICKETS SOLD OUT!!!
Price of the bus ticket is 15€ (same price more or less than the train but with the security that your place for the bike is booked). Above of this, the trip is faster. Departure will be between at 19:00 and arrival will be in França train station in Barcelona at 20:00 aprox. (same place of departure of the ride).
2. By taxi: the guys of Gironataxi have 3 vans of 8 seats with trailer for bikes. They offer a taxi service from Girona to Barcelona in the morning as well. Book on telephone number: 649 852 454
3. By train: there’s minimum one train per hour on Sundays afternoon (check here the timetable). But access to the train for the bike is not guaranteed even if you buy a ticket for your bike. It’s a decision of the train reviewer if your bike can get in or not. Can you take the risk?
4. on your own: that means that somebody can pick you up, or leave a car in Girona before o go back to Barcelona or wherever by bike.