I slipped up.  I spent the weekend building a 12 x 8 pent roof shed.  I felted the roof and put barge boards all round.  I've now put the guttering up, but alas, I put the rear barge board over the felt, so I now have the gap for the rain to fall down before it even gets to the guttering.

School boy error, I know.  I can hear you all tutting......

Can anyone advise the best solution for me?  Can I buy something adhesive to stick to the bottom 6 inches or so of the felt, which will carry on over into the guttering?

Thanks in advance.