So I've recently started trading and I feel like I must be leaving out one (probably glaringly obvious) step. I've looked through the forum and couldn't see anything that answered my question specifically. Any help for a noob would be greatly appreciated. This is what I'm doing:

-Getting both back and lay matched a tick or two apart using back and lay columns @ $5
- I've also tried using the dedicated profit/loss column. I've also used the API.

In all cases this happens:

-Profit or loss goes unbolded green/red.
-Shortly after, profit/loss re-bolds and payout value starts to move again. It's not locking it in.

If I watch it in betfair, shortly after greening up, geekstoy puts on another smaller bet. If I do the scalp in GT then switch screens to BF, I can use the cash out function, which it does. But then GT places another smaller bet, putting me back in the running and giving me the option to cash out in BF again (from my understanding). Once my profit's locked in, shouldn't it stay that way? Or am I doing something wrong?

As I said, any help would be greatly appreciated as I'm fairly lost at this point. I've posted pics below to help describe what I mean.

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