The obsessive thought that moving my hand carelessly would give me away assaults me.
Literal
Clumsily hand [object-を] move-[conditional-と] noticed-[regret-てしまう] [called-という] obsessive-thought [subject-が] me [object-を] attacks.
強迫観念 ('obsessive thought, compulsion') is a psychological term — 強迫 'coercion/obsession' + 観念 'idea/concept.' The sentence personifies the thought with 襲う ('to attack, to assault'), making the anxiety feel like a physical threat. 下手に ('clumsily, unwisely') warns against careless action — a small move could give the speaker away.