wildflower lawn

Hi, I would be really grateful for any advice/reassurance on something. I am trying to create a nature trail around a large garden and I thought a great feature would be a wildflower lawn. earlier in the year I made the garden pond deeper and piled up all the soil I dug out of the bottom. Thinking this was likely to be the least fertile soil in the garden, I chopped out a section of lawn and spread this soil over the space (about 2 or 3 inches thick). It was quite thick and sticky with an orangy colour so I assume it was clay. There was also quite a bit of sand in it which was originally used to cushion the pond liner. I sowed a grass and flower seed mixture (for 'most soil types') over it the other day (late October), raked it in and trampled over it to let the seed contact the soil properly. The next day it rained cats and dogs and I noticed the soil wasn't draining that well and lots of puddles were forming on the surface. I am wondering if this soil was in fact at all suitable for this purpose and would a winter of virtual water logging affect the germination rate in the spring? Many thanks for your thoughts?