Do I have to testify at my own trial?

No. The decision belongs to you, not to your attorney, but it should be made with counsel's advice — and the advice is often not to.

What testifying opens. Cross-examination by the prosecutor. In most circumstances, the ability to impeach you with certain prior convictions, which may otherwise never reach the jury. And the risk that a nervous, imprecise, or defensive answer becomes the thing jurors remember.

What it can provide. In some cases the defense requires the defendant's account — self-defense being the clearest example — and no one else can give it.

What not testifying costs. Less than people fear. The jury is instructed that the decision cannot be held against you, and the State cannot comment on it.

The honest framing: most defendants who testify do not improve their position. Some must. Which category you're in depends on the specific case, and the decision is generally made late, after the State's case has been heard.