CCS/MSP430F249: I2C SCL/SDA timing problem

I wrote a code like below
//main.c
int main(void)
{
    Grace_init();                   // Activate Grace-generated configuration
    
    while(1)
    {
    	while (UCB0CTL1 & UCTXSTP);             // Ensure stop condition got sent
		UCB0CTL1 |= UCTXSTT;                    // I2C start condition
		while (UCB0CTL1 & UCTXSTT);             // Start condition sent?
		UCB0CTL1 |= UCTXSTP;                    // I2C stop condition
		__bis_SR_register(CPUOFF + GIE);        // Enter LPM0 w/ interrupts
    }

    // >>>>> Fill-in user code here <<<<<
    
}

#pragma vector=USCIAB0TX_VECTOR
__interrupt void USCI0TX_ISR_HOOK(void)
{
    /* USER CODE START (section: USCI0TX_ISR_HOOK) */
	RXData = UCB0RXBUF;                       // Get RX data
    __bic_SR_register_on_exit(CPUOFF);        // Exit LPM0
    /* USER CODE END (section: USCI0TX_ISR_HOOK) */
}