TM4C123GXL ADC problem

I am trying to sample to sample a 50 Hz sine signal using a timer trigger. The timer has a period of 1000 Hz. The problem is that my output looks nothing like the signal coming in.

Below is my code and corresponding graph---

uint32_t Voltage;
uint32_t pui32ADC0Value[1];

void
InitConsole(void)
{

    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOA);
    GPIOPinConfigure(GPIO_PA0_U0RX);
    GPIOPinConfigure(GPIO_PA1_U0TX);
    SysCtlPeripheralEnable(SYSCTL_PERIPH_UART0);
    UARTClockSourceSet(UART0_BASE, UART_CLOCK_PIOSC);
    GPIOPinTypeUART(GPIO_PORTA_BASE, GPIO_PIN_0 | GPIO_PIN_1);
    UARTStdioConfig(0, 115200, 16000000);
}


int
main(void)
{
    uint32_t ui32Period;
    //Set Timer0
    SysCtlClockSet(SYSCTL_SYSDIV_1|SYSCTL_USE_PLL|SYSCTL_XTAL_16MHZ|SYSCTL_OSC_MAIN);
    SysCtlPeripheralEnable(SYSCTL_PERIPH_TIMER0);
    TimerConfigure(TIMER0_BASE, TIMER_CFG_PERIODIC);
    ui32Period = (SysCtlClockGet()/1000)/2 ;
    TimerLoadSet(TIMER0_BASE, TIMER_A, ui32Period-1);
    IntEnable(INT_TIMER0A);
    TimerIntEnable(TIMER0_BASE, TIMER_TIMA_TIMEOUT);
    IntMasterEnable();
    TimerEnable(TIMER0_BASE, TIMER_A);

    InitConsole();

    SysCtlPeripheralEnable(SYSCTL_PERIPH_ADC0);
    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOE);

    GPIOPinTypeADC(GPIO_PORTE_BASE, GPIO_PIN_3);

    ADCSequenceConfigure(ADC0_BASE, 3, ADC_TRIGGER_PROCESSOR, 0);
    ADCSequenceStepConfigure(ADC0_BASE, 3, 0, ADC_CTL_CH0 | ADC_CTL_IE |ADC_CTL_END);

    ADCSequenceEnable(ADC0_BASE, 3);
    ADCIntClear(ADC0_BASE, 3);
    ADCIntEnable(ADC0_BASE, 3);

    while(1){
    }

}
void timer_ADC(void)
{
ADCProcessorTrigger(ADC0_BASE, 3);
while(!ADCIntStatus(ADC0_BASE, 3, false)) ;
ADCSequenceDataGet(ADC0_BASE, 3, pui32ADC0Value );
Voltage = (pui32ADC0Value[0]*3.3/4096);
}
void
Timer0IntHandler(void) {
    TimerIntClear(TIMER0_BASE,TIMER_TIMA_TIMEOUT);
    timer_ADC();
    UARTprintf("%4d\r", pui32ADC0Value[0]);
}