If you have a spare room, pot up a sensible selection from all the seedlings into three inch diameter pots, fit a wallpaper table or three in the room (any fold up table will do) with a suitable waterproof surface on them and fit some "growlights".
These lights can be expensive and burn lots of 'lecky.
I stress the words "sensible selection" as what you pot up will get bigger and need potting up again later in the year. This way you can salvage something ready for an early start. Some folk say that a potbound seedling will be slower to get away than a fresh seedling, but it is worth doing some.
Please do not be too enthusiastic about purchasing lots of the lights, or you may get visited by your local drug squad.
Where you went wrong?
You got it all right.
Perfect germinating conditions, remember what you did for a few months time.
