Buy-Short-same-bar-with-single-position

CODE:

using WealthLab.Backtest;
using WealthLab.Core;
using WealthLab.Indicators;
using System.Drawing;

namespace WealthScript1 
{
    public class MyStrategy : UserStrategyBase
    {
        //Initialize
        public override void Initialize(BarHistory bars)
        {
         channelLow = EnvelopeLower.Series(bars.Low, 5, 0, EnvelopeMAType.EMA);
         channelHigh = EnvelopeUpper.Series(bars.High, 5, 0, EnvelopeMAType.EMA);
         PlotTimeSeriesLine(channelLow >> 1, "Channel Low", "Price", Color.Green, 1);
         PlotTimeSeriesLine(channelHigh >> 1, "Channel High", "Price", Color.Red, 1);
        }

        //Execute
        public override void Execute(BarHistory bars, int idx)
        {
         if (LastPosition?.PositionType == PositionType.Long)
         {
            PlaceTrade(bars, TransactionType.Sell, OrderType.Stop, channelLow[idx]);
            PlaceTrade(bars, TransactionType.Short, OrderType.Stop, channelLow[idx]);
         }
         else
         {
            PlaceTrade(bars, TransactionType.Buy, OrderType.Stop, channelHigh[idx]);
            PlaceTrade(bars, TransactionType.Cover, OrderType.Stop, channelHigh[idx]);
         }
        }

      //private members
      private IndicatorBase channelLow;
      private IndicatorBase channelHigh;
    }
}