+xHi Sam,
27C is a bit too warm for such a thick pour with wood - the wood insulates the resin so its hard for the heat to escape so the slight waveyness may well be the heat. However, other than that there looks to be no damage so shouldn't be an issue.
In terms of layering over the top, you need to key the surface with a 240 grit paper then clean all the dirt off before pouring. The new resin fills in the scratches on the surface so you should retain the clear finish.
Great to hear, 240 grit it is. Thanks Warren