No matter how high the wall is, even I was scared at first, you know.
Literal
No-matter-how wall [subj-が] high [although-といっても], I [also-も] beginning [topic-は] timidly [copula-でしたよ].
いくら~といっても 'no matter how much X / even though X' is a concessive construction. おっかなびっくり is a fun compound expression meaning 'timidly / gingerly / nervously doing something' — literally 'scared-surprised.' 最初は 'at first' sets the temporal contrast with the implied current confidence.