Rough-in storm drain in 12” slab - help

I am getting a 12” slab poured about 9’ below grade. The contractor agreed to let me do the drainage to save some money. However, I’ve run into a possible issue. [This](https://www.homedepot.com/p/U-S-TRENCH-DRAIN-18-in-x-14-in-Storm-Water-Pit-and-Catch-Basin-for-Modular-Trench-and-Channel-Drain-Systems-with-Aluminum-Grate-80072/303526931?cm_mmc=ecc-_-THD_ORDER_CONFIRMATION_BOSS_STH-_-V1_M1_CB-_-Product_URL&ecc_ord=WM76984380&em_id=d28cd6addc4e4a4597fb8d839750acd4b4c84fb2e254786a39b4dc2645604847) is what I’m going to rough-in; but if I go with the sharp corners, then that’s more likely that the concrete will crack right?? So how would you build the form for this??