Timer Skips a Second

Hey guys,

I'm trying to get my timer to measure seconds but it skips two seconds if I press stop and three times if I press stop again etc.

        
timer = new DispatcherTimer();
ts = new TimeSpan(1000000);
timer.Interval = ts;

   private async void btnBegin_Click(object sender, RoutedEventArgs e)
        {
            if (hasBegun == false)
            {
                if (cmbxSubjects.SelectedValue != null && cmbxActivities.SelectedValue != null)
                {
                    timer.Start();
                    timer.Tick += timeData_Tick;
                    btnBegin.Content = "Stop";
                    hasBegun = true;
                    btnLogSession.IsEnabled = false;
                }

                else if (cmbxSubjects.SelectedValue == null || cmbxActivities.SelectedValue == null)
                {
                    await pleaseEnterAllFields.ShowAsync();
                }
            }

            else
            {
                btnLogSession.IsEnabled = true;
                btnBegin.Content = "Start";
                hasBegun = false;
                timer.Stop();
            }
        }

        public void timeData_Tick(object sender, object e)
        {
            if (seconds == 60)
            {
                seconds = 0;
                lblSeconds.Text = seconds.ToString();
                
                minutes++;
                lblMinutes.Text = minutes.ToString();
            }

            else if (seconds < 60)
            {
                seconds++;
                lblSeconds.Text = seconds.ToString();
            }

                if (minutes == 60)
                {
                    minutes = 0;
                    lblMinutes.Text = minutes.ToString();

                    hours++;
                    lblHours.Text = hours.ToString();
                }

                totalSeconds++;
        }

How can I fix it?