I have attempted 2 official NMAT mocks and scored 225 and 228 respectively. Is that a good enough score?

If targeting top colleges then NO. If other than top colleges are on the list then YES

what is the cutoff for gk in XAT

there is no cutoff for GK as this section is not considered for percentile calculation but it will be considered in the final list

varc-dm-qa = 10-10-12 (for safer side)

in va 9 to 10 is on safer side in Dm 11 and in quant 13/14 as on previous cuttoffs and rest we dont know about the difficulty level of the exam.

Surely you will get a call from NMIMS Mumbai. All the best buddy.