What if I under / over-bid my T-Bills for competitive bid

Hi everyone, for this coming T-bill's auction, what would happen in the following scenarios where competitive bid is selected:

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1) What if the yield is 4% but I indicated 3.8% yield, will I be allocated 3.8% yield or 4%?

2) What if the yield is 4% but I indicated 4.2% yield, will I be allocated 4.2% yield or 4%?

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Thanks in advance all!