According to your code, individual items of ErrorTable contains the List of Mem, Err , ErrMon, MemMonth.
Thats why it is showing like that.

I could think to write this code as below.

1. Create a WrapperClassIndivialItems class which will hold individual items.

public class WrapperClassIndivialItems{
    	public integer Mem {get; set;}
        public integer Err {get; set;}
        public String Errmon {get; set;}
        public String MemMonth {get; set;}
            
        public WrapperClassIndivialItems (String ErrorMonth, String Memmonth, Integer Memberships, Integer Errors){
            Mem = Memberships;
            Err = Errors;
            ErrMon = ErrorMonth;
            MemMonth = MemMonth;
        }     
    }

2. I will change the getWrapperC() code as below, it will return a List<WrapperClassIndivialItems>
3. Create a Map wrapperMap like this which will hold row count and row of individual item.

Map<Integer,WrapperClassIndivialItems> wrapperMap = new Map<Integer,WrapperClassIndivialItems>();

4. Populate the map in the loop.
5. return the List<WrapperClassIndivialItems> from Map.
 

public list<WrapperClassIndivialItems> getWrapperC(){

        list<AggregateResult> MembershipAggList = new list<AggregateResult>([SELECT SUM(New_Memberships__c) Memberships, Calendar_month(event_date__c) EventMonth FROM Campaign WHERE Facilitated_By_MD__C = '005i0000000z0nW'GROUP BY Calendar_month(event_date__c )]);  
        list<AggregateResult> ErrorAggList = new list<AggregateResult>([SELECT count(ID) Errors, Calendar_month (App_sign_Date__c) Datemonth FROM Missing_Info_Errors__C WHERE Officer__c = 'John Smith' AND App_Sign_Date__c = THIS_YEAR GROUP BY Calendar_month(App_Sign_Date__c)]);
        
       	//list<integer> MembershipIntList = new list<integer>();
        //list<string> MemMonth           = new list<string>();
        //list<string> ErrorMonth         = new list<string>();
        //list<integer> ErrorIntList      = new list<integer>();		
		//list<WrapperClass> ErrorTable = new list<WrapperClass>();
		
        Map<Integer,WrapperClassIndivialItems> wrapperMap = new Map<Integer,WrapperClassIndivialItems>();
		Integer rowNum = 1;
		
        for(AggregateResult m : MembershipAggList){
        	//MembershipIntList.add(integer.valueOf(m.get('Memberships')));
            //MemMonth.add(string.valueOf(m.get('EventMonth')));
			wrapperMap.put(rowNum, new WrapperClassIndivialItems(null, string.valueOf(m.get('EventMonth')), integer.valueOf(m.get('Memberships')), null));
			rowNum++;
       	}
        rowNum = rowNum -1;
		
		
		Integer iCount = 1;
        for(AggregateResult e : ErrorAggList){
			if(iCount<= rowNum && wrapperMap.size()>0)
			{
				WrapperClassIndivialItems wrObj = (WrapperClassIndivialItems)wrapperMap.get(iCount);
				wrObj.Err = integer.valueOf(e.get('Errors'));
				wrObj.ErrMon = string.valueOf(e.get('DateMonth'));
			}
			else
			{
				wrapperMap.put(iCount, new WrapperClassIndivialItems(string.valueOf(e.get('DateMonth')), null, null, integer.valueOf(e.get('Errors'))));
			}
        	//ErrorIntList.add(integer.valueOf(e.get('Errors')));
            //ErrorMonth.add(string.valueOf(e.get('DateMonth')));
			iCount++;
        }
        return wrapperMap.values();
		
        //ErrorTable.add(new WrapperClass(ErrorMonth, MemMonth, MembershipIntList, ErrorIntList));
            //return ErrorTable;
        
    }

Please note that I have not compiled the code, but tried to put my thoughts into it.

Let me know if it serves your purpose. and if so then mark this answer.