I am neither a geologist, nor a planetary scientist, however, I do have some technical knowledge of both fields (which includes a sizable amount of cratering). At first glance, this doesn't seem all that likely-craters tend to make big bowls.

HOWEVER!

Upon thinking a little bit, I recalled several basic facts about large craters (as you have):

1) They tend to have ring structures and a central peak in the middle of them-sometimes several rings.
2) The edges tend to be uplifted, and the bottom of the crater (if it is a large crater) is usually pretty flat
3) They CAN cause extensional cracks (radially outwards from the crater), but this effect is much smaller (read less wide- the length of the cracks actually seems about right) than what you have shown with the various landmasses in your map, even with an impact of that size.

For example, here's an image of the crater Orientale on the Moon:


(The reason I chose Orientale is because most other large impact basins are filled in with lava or are old enough that the structure is eroded).

So, really the only major geological problem with the crater here is that the 'spiderweb cracks' are just too large. I think you could explain that away by saying that over the eons, rivers and other weathering have eroded the extensional cracks so that they're extremely large. Cool concept, I think you should run with it!