Rates will likely start to rise early next year, fix now for as long as you can IMO, especially if your current rate is 3.8%. I can't post a link here to where to view historical swap rates but google 'the ice swap rates' and you'll find it.
Inflation is not hitting the targets the ECB have set, they indicated during the week that QE may have to go on for longer than anticipated.
Therefore i think it is doubtful that rates will rise next year.
The truth is that nobody knows the future, even the future direction of interest rates.
I could say that your guess is as good as anybody else's but actually that is not likely to be true. It is likely that the banks guess is better than yours. That is why it is foolish to try to out guess the bank. Especially to bet your mortgage on your attempt to out guess the bank.
If a guaranteed 2.75% for 3 years is attractive to you with certainty around the amount of the payment then go for it. But know that either way you cannot be sure in advance that you have chosen the cheapest option.