Hi guys - I knitted my first beret but I used wool that I thought looked the same as my pattern but must be slightly bigger or stretchier so it’s too big and floppy.
Anyway can I dip it in hot water to shrink it a bit? Any advice welcome.
Thanks,
Tavs 
Are you familiar with the felting process?? If not, what you do is put your item in a washing machine with HOT water along with a few pairs of old jeans and let it go, watching closely so it doesn’t shrink too much. I would not recommend you doing a full-felting on your hat, but you might get good results from lightly felting it, and by this I mean maaaaybe a few minutes in the washer but no more than that. It also depends on your washer, how hot your water is, and how big the item is, but I’ve gotten good results shrinking items slightly using this method.
Just a note that this will only work is your item was knit with a natural fiber. Acrylic, cotton, etc. do not felt. It’s it’s 100% wool it will.
If you can’t shrink it, perhaps you could make an elastic edge by getting some elastic and threading it through a casing made by extending the edge a bit. Fold it over and sew it down. It will be a Baggy Beret which stays attached to your head, but is big enough to tuck your dreadlocks in! (I can’t think of the name of this sort of hat… but I’m sure there is one)
Thanks for the advice folks - will give the felting a go and if that doesn’t work will start on the dreadlocks!
thanks
If you felt it a bit harder, it will look pretty shrivelled at first, but a vigorous tug over a dinner plate will put all right again. The dinner plate will give it a nice crisp shape and let you shape the brim carefully. Balance the dinner plate on a cup or bowl so air can circulate all around and the brim won’t get crushed or crimped.
I’ve had a beret or two that I thought I felted too far, 
but they were easily brought back by tableware, a firm hand and a determined attitude. Whew!