I recommend reading Cryptography Engineering [0] and then re-evaluating the design and then get it audited. I took that path and I learned a ton and still had (some smaller) issues in the audit.
Cryptography Engineering was great for its time but has been outdated for years, which in cryptography doesn’t mean “lacks fancy new stuff” but “we learned the hard way to do things differently”. Serious Cryptography and Real World Cryptography are commonly mentioned as successors.
