、。。
That's surely a misunderstanding. You're overestimating me.
Literal
That [topic-は] surely, misunderstanding [copula-だ]. You [topic-は] me [obj-を] overestimate-[-てる].
きっと 'surely / certainly / without a doubt' is a confident adverb, often softened to 'I'm sure...' in conversation. 誤解 'misunderstanding' is a formal sinitic compound. 過大評価 '(to) overestimate' is a four-element compound 過大 'excessive' + 評価 'evaluation,' which in combination with する gives a single verb. ~てる (casual い-drop of ~ている) marks the state of currently overestimating.