"Fuel tank retainer ring" gasket?

hi guys, when i open the fuel tank under the boot and than i fitted the retainer ring and gasket back, i noticet,that when i across a 3500rpms ,i smell a lot of fuel fumes from the rear of the car. Maybe i put the seal wrong and somewhere it can blow. Do you have experience with changing the seal?Because in ETK isnt any mentioned the gasket....

Thank you