By which I mean on the inside of the house still. OBVS.

I bought some that I measured up wrong and are too narrow but looking at exchange options the next pair up are 20 cms too long. The bit they attach to looks as though it must be fitted on the inside of the frame? I don't have a sewing machine and do not fancy cutting them up and trying to hem them by hand so can they be fitted on the outside of the window frame - on the internal wall if you know what I mean...

It's these ones if this helps...

http://www.dunelm.com/product/blackout-roller-blinds-1000001910?cmCategoryId=34151#30077459