Probably you mixed-up the conception of Treasure Bill Pricing with Treasure Bill Futures Pricing

Treasure Bill Pricing:

In U.S. T-bills and other zero-coupon bonds are quoted in yields, not prices. Avery special way of quoting T-bill yield is used:   the bank discount yield.

Let us note:

•         P:         market price of the discount instrument

•         F:         par value, assuming 100

•         D:        dollar amount of the discount in price (F - P)

•         yd:       annualized yield on a bank discount basis

•         n:         number of days remaining to maturity

The equation of pricing is

P= F*[1-yd(n/360)]

The relation between D and yd is

yd=(D/F)*(360/n)=(F-P)/F*(360/n)

D=(n/360)*(yd*F)