Placing a trade and it is immediately negative?

I’m new to trading and have had this happen twice.
I place a trade in the middle of a candle and it turns immediately negative.
My example this morning was the GBP/CAD.
I shorted it in the middle of a red/short candle and when it clicked on, it immediately read -20.1.
Was this due to the Bid/Ask?
And how do I use the Bid/Ask to my advantage?
Thank you!
I really appreciate the help.

Do u mean Spread !?

Yes, this is because of the bid/ask spread. When placing market orders:

Going short - your position will be opened @ the Bid price
To close a short - you need to buy @ the Ask price

Going long - your position will be opened @ the Ask price
To close a long - you need to sell @ the Bid price

Spread and slippage will cause this to happen. Also less traded pairs have bigger spread so you’ll see this more often on such pairs instead of like EUR/USD.

Thanks so much!
That really helped.
I figured that out later in the day but so appreciative to have a clean, clear response.
Thanks again.

More specifically, most of it was perhaps due to a Bank Holiday spread? It [I]is[/I] Good Friday … not generally regarded as a “trading day” …

Yes, it happens because of spread and slippage. That said, sometimes the market also moves a little against you, which is a random occurrence, obviously.