mullibum wrote:

We got a tree, planted three years ago, and it's just
started to bud,

I'm not sure what you mean by "budded", all trees have buds at all times
throughout their life.

it needs to be cut back.

Why, who says, and how much?

If I cut it back will it get ruined?

What do you mean by ruined, appearance, health? When done correctly pruning
will improve a tree... all trees require and benefit from periodic pruning.
No one can answer your question with specifics until you at very minimum
identify the tree to which you're refering