gst composition scheme

hello experts
my one client is fall under 1% composition scheme for retail shop now he doing catering business also and provide food to hostel which amount credited in his current a/c so now he is liable for 5 % for food providing service and 1% for his retail shop or he should continue in 1 % and if he continue 1 % and if notice comes for this so how much maximum penalty he is liable to pay for wrong gst rate paid