On the bright side, it will grow back. In future though, in order to have the best experience at the barber's/hair salon, you want to be extremely specific about what you want. "A bit of a trim" is too subjective to guarantee getting the cut you want.
The best thing you can do is have a picture of the exact style you want for the stylist to reference, and if you don't have that, at least know the exact length you want your hair to be at each section in inches/centimetres/millimetres, or know exactly how much length you want the stylist to cut off. When you get a haircut that you like, take a picture to show the stylist for the next time
Also, hair grows approximately 0.5 inches per month, so say you get a cut you like and you go back three months later wanting the same cut, you'd ask for the stylist to take 1.5 inches off.