Sales entry for Cement trading

Sir.

I purcahses Cement of  rs 150000 @ 300 per bag  including transport but company says to sell at 250 for which I get credit note of 30 rs and 20 rs is retained by company and increase my credit limit but in tally if I sales at 250 after a purchase at 300 and getting credit note of 30  tally show loss so the retained amount entry in which head should be done as it's not a loss to me because my amount is with company