It will almost certainly grow wider without any help from you . . . ours is about 5ft tall and the same width. The received wisdom is never to prune an Acer except for removing damaged or diseased branches.

I'm not sure your Acer is going to be happy in pot long term and you are going to need to repot every year to start with. By now it is in full leaf so it is a little late to repot but do so carefully and keep well watered once you have repotted.

Hi and thanks Shielabub, I presume yours is in a pot too.
How long have you had yours?

Thanks Moon Grow, my garden's a bit crowded with shrubs and trees. Hard to find a permanent place that's suitable so a pot is more flexible.

Hi Pinky, ours is in a raised bed, in peat-based compost, and planted there about 10 years ago. Acers are very slow-growing.

Well it is your Acer but it isn't going to be happy for any length of time in a pot - sorry.

Acer look lovely in pots but tend to find after about 5 years start to look a bit tired, but I would certainly put it in a nice ceramic pot it should be happier in that, I've put mine in John Innes No 3 compost then put some gravel on top of compost to set it off. I had Bloodgood in a pot then made room in the garden after about 5 years. See my photo on bottom of page 14 of my pics if you wish :-))