How to prevent floating point excel data loaded with SQL to be truncated

DataTable part8 = new DataTable();
part8 = loadData(path, "SELECT * FROM [Gaszähler$X13:Y]");
Console.WriteLine(part8.Rows[10][1]);

private DataTable loadData(String path, String command)
{
    String filepath = path;
    String db_command = command;

    OleDbDataAdapter adapter = fetch(filepath, db_command);
    DataSet set = new DataSet();
    DataTable returntable = new DataTable();
    adapter.Fill(set, "table1");
    returntable = set.Tables["table1"];

    return returntable;
}

public OleDbDataAdapter fetch(string filepath, string com)
{
    OleDbConnection conn = new OleDbConnection(); // Die Verbindung
    string ConStr = // Der Connectionstring
         @"Provider=Microsoft.ACE.OLEDB.12.0; Data Source = " + filepath
        + @";Extended Properties=""Excel 8.0;HDR=Yes;IMEX=1;ImportMixedTypes=Text;TypeGuessRows=0""";

    conn.ConnectionString = ConStr; //Der Connectionstring wird gesetzt

    OleDbCommand command = new OleDbCommand // Das OleDb Kommando
        (
            com, conn
        );
    OleDbDataAdapter myAdapter = new OleDbDataAdapter(command); // Ein Adapter

    return myAdapter;
}