Hi Jony, hmmmmm ! but my gut feeling is that you might just have got away with it as most weed and feed rely on there being existing weeds present in grass on which the chemicals act. So assuming that as it had only been sown recently and that its been dry (assuming that your in the UK ??) IF nothing had germinated, you probably are ok but if the seed had germinated, then it might be a different story ?? Also, most weed and feed require that the lawn is at least 6 months old before applying so if even the grass has germinated, you might have damaged that as well !! I think you'll need to see what happens and what grows ??
As a point of interest, having created several 'wild meadows' professionally, if I was to be asked whats the biggest mistake that most people make, its trying to create these in 'normal top-soil', let me explain. If you do try to create these in normal top soil, the grass grows so well that it often smothers the broad leaved flowering element of the mixture and you end up with very little 'flower' so what I found was the most successful way is to remove most of the top soil almost to subsoil level and then sow. The effect of doing this is to 'weaken' the grass element, allowing the flowering element more chance to survive without the grasses crowding them out.
One of the most successful 'wild flower meadows' I ever created was on coastal sand dunes, as planting here gave a lovely balance to the grass v wild flowers, due to the poor nature of the sandy soil.
Hope this helps, Lannerman.