Liquidity issue in Future shares with few lots only, I am new, give tips, how to sell?

I do BTST trades in some stocks like DALBHARAT, WHIRLPOOL, IEX, IOC on Nov Fut.

I buy 3-4 lots for each stock. But when I try to sell them in the first minute of market open, I usually pay 0.05 to 0.2% extra on my “last lot sell” compared to “first lot sell”.

For example,

First Lot sell of Whirlpool is sold for 2292 and 3rd lot is sold for 2288.6, hence paying an extra 0.15%.

This 0.15% extra is a lot, and kills my profit. I am just buying few lots.

I am also noob, so I either directly sell all lots in 1 order or sell 1 lot every 5 second at market price, but nothing seems to be working.

Big players trade with 100+ lots in a single stock, how do they manage to exit their position with least chances of loss like this.