Why does this algo not initiate sell orders from this code?

import datetime

from datetime import timedelta

class BollingerBreakoutAlgorithm(QCAlgorithm):

def Initialize(self):
self.SetStartDate(2019, 1, 1)
self.SetEndDate(2019, 11, 25)
self.SetCash(100000)
self.AddEquity("UNH", Resolution.Daily)
self.Securities["UNH"].Price
self.bband = self.BB("UNH", 20, 2, MovingAverageType.Simple, Resolution.Daily)
self.SetWarmUp(364, Resolution.Daily)
self.SetBenchmark("SPY")
self.ticket = None
self.period = timedelta(days=3)

def OnData(self, data):
if not (self.bband.IsReady): return
price = self.Securities["UNH"].Price
if price <= self.bband.LowerBand.Current.Value:
self.MarketOrder("UNH", 20)
self.ticket

if self.ticket is not None and (self.UtcTime > (self.ticket.Time + self.period)):
self.Liquidate(self.ticket.Symbol)
self.ticket = None