Hi,
I assume you placed the buy order today?
If so, Freetrade will schedule the buy order to execute on Monday at some point after the market opens.
At that point, they will buy as many shares as they can with the £2000 at the prevailing price and any remaining money will be placed back into your account.
You should see the pending order on your main account screen.
If you want you can cancel your buy order and just execute it again when the market opens and you will immediately have access to the remaining money as the trade should execute immediately.