I live in the UK (south) and planted cucumbers indoors. Did I plant them too early?
I normally wait til mid-March ....they germinate quickly and can get leggy if I start earlier than that. You can try and keep them going by turning them lots (so they don't bend to the light) or you can have another go in a few weeks time
I sow them in the second half of March too, even April if it's cold. You do mean sowed the seeds, not planted little plants that you bought? Some garden centres are selling young plants far too early.