If your prediction is correct
The pound rises against the euro, and GBP/EUR is now trading at 1.1309, with a buy price of 1.1310 and a sell price of 1.1308. You reverse your trade to close your position, so you sell three contracts at 1.1308.
Your £300,000 is now worth €339,240, because 1.1308 x (100,000 lot size x 3 CFDs) = €339,240. €339,240 – €338,550 = €690, which is your profit from the trade. You could also calculate this as 11308 – 11285 = 23, which you multiply by €30 per point to get €690.
As ever, you’d have had to pay funding charges if you kept your position open overnight – and you’ll also have to pay capital gains tax on any profits.