error EA when run

hello, My EA auto buy or sell on Gold terminal. When orderbuy or ordersell is close, the lots is higher lots orderbuy or odrersell . I don't know why Max lots orderbuy or ordersell  EA can create is 0.02. How can i to get a lots (0.04,0.08...) Thanks

This is my EA

//+------------------------------------------------------------------+ 
//|                                                 Experts test.mq4 | 
//|                        Copyright 2017, MetaQuotes Software Corp. | 
//|                                             https://www.mql5.com | 
//+------------------------------------------------------------------+ 
#property copyright "Copyright 2017, MetaQuotes Software Corp." 
#property link      "https://www.mql5.com" 
#property version   "1.00" 
#property strict 
 
 
extern double pointbuy = 1290; 

//+------------------------------------------------------------------+ 
//| Expert initialization function                                   | 
//+------------------------------------------------------------------+ 
int OnInit() 
  { 
//--- 
 
//--- 
   return(INIT_SUCCEEDED); 
  } 
//+------------------------------------------------------------------+ 
//| Expert deinitialization function                                 | 
//+------------------------------------------------------------------+ 
void OnDeinit(const int reason) 
  { 
//--- 
    
  } 
//+------------------------------------------------------------------+ 
//| Expert tick function                                             | 
//+------------------------------------------------------------------+ 
void OnTick() 
  { 
//--- 
   string sym = "Gold"; 
   int cmdbuy = OP_BUY; 
   int cmdsell = OP_SELL; 
   double lot = 0.01; //lot 
   double b = 5.11; // check lot 
   double c = 2; // x lot 
   double buy = Ask; 
   double sell = Bid; 
   double stoploss_ask = Ask - 5; 
   double stoploss_bid = Ask + 5; 
   double takepropit_ask = Ask + 5; 
   double takepropit_bid = Bid - 5; 
   int magic = 155; 
   Comment(" phien ban 1"); 
   
  while(lot < b) 
   { 
       while( Ask > pointbuy && OrdersTotal()==0) 
       { 
        int newbuy = OrderSend(sym,cmdbuy,lot,buy,NULL,stoploss_ask,takepropit_ask,NULL,magic,NULL,SYMBOL_ARROWUP);  
            if(  OrdersTotal()==0) continue; 
            lot=lot*c; 
            Comment ("LOT "+ (string)lot) ; 
        } 
       while( Bid < pointbuy && OrdersTotal()==0) 
       { 
         int newsell = OrderSend(sym,cmdsell,lot,sell,NULL,stoploss_bid,takepropit_bid,NULL,magic,NULL,SYMBOL_ARROWDOWN); 
         if( OrdersTotal()==0) continue; 
            lot=lot*c; 
            Comment ("LOT "+ (string)lot) ; 
       } 
      
      } 
  } 
//+------------------------------------------------------------------+