Constitutionally you are correct. However, the Federal Register is approximately 4 times larger than the US Code. That is four times more rules that are enforced like laws than actual laws passed by Congress. Additionally, agencies are under the Executive that is explicitly prohibited from making laws.

Congress in many respects has abdicated it lawmaking authority to the Executive by creating administrative agencies. Violating agency rules will not land you in a court with a jury of your peers as required by the Constitution either. You will end up in a court run by the accusing agency with a judge appointed by the agency. But hey, they aren't laws just rules with criminal and financial penalties for violating them.