Never mind being too early to plant seed directinto grow bags - it's something you don't do anyway!!!
You need a decent plant to pop into a bag, that way you know there's going to be a plant where you want it.
Whitelady is right - start them inside on a window sill. I put mine in a seed tray, (24 seeds to a half size tray), cover with glass or polythene, then cover that with newspaper to keep out the light.
As soon as the first one shows, take off the covering, tuck a bit of cooking foil part way under the seed tray, on one long side, then bring up the back & sides vertically, leaving one long side exposed. (If this makes sense). The foil should be 3" to 4" longer than the seed tray on each side. What you should end up with is a vertical piece of foil behind the tray and for a certain length on each side.
This will increase the amount of light the plant gets & stop it becoming 'drawn'. Keep in the window sill, obviously with the exposed side of the seed tray facing the window.
After the second set of leaves is well formed, pot up into 3" pots, keep in window sill until it's consistantly reasonably warm at night, (unless the greenhouse is heated), not forgetting to come up with some cunning plan to keep the foil in position. I grow mine in a small upstairs window and 'blue tac' the foil across the ledge.
Hope this helps and is not too confusuing. The foil bit is easy to do, not so easy to write down!!!