There are two variants of Grincoin mining. CuckARoo (for GPU only & 6+GB VRAM) and CuckAToo (for ASICs & GPU w/ 11+ GB VRAM)
Now you are mining CuckARoo31 and as you can see from the pool given below, a 1080ti can do around 0.551 g/s which is less then what your rig is capable of.
https://pool.btc.com/Anyway, Grincoin uses Graphsize as a parameter rather than Hashes which most of PoW coins use.
So the unit is graphs per second (g/s) rather than hashes per second (h/s)
So, the conclusion is, there is no problem with your configuration.