I'm guessing you meant to show North bidding 3
♣ in your bidding diagram, not 3
♦.
I don't know where you get the idea that 3
♦ would be unethical. Why?
What you could and should have done is call the director. He would give your LHO the opportunity to accept your 1
♦ bid, in which case the auction would have proceeded normally from there. If LHO did not accept 1
♦, you would be required to substitute "a legal call" (Law 27B). One purpose of calling the TD is to ensure that the rights of
both sides are protected.
One could argue that it is unethical not to call the TD: Law 10 says "The Director alone has the right to determine rectifications when applicable. Players do not have the right to determine (or waive see Law 81C5) rectifications on their own initiative." So correcting your IB on your own is illegal and if you know it's illegal, it's unethical.
Generally speaking, once a side has "paid" the rectification for an infraction, they can do what they want, subject to UI constraints, even if they appear to gain advantage thereby (Law 10C4). In the case of an IB, though, the TD is required to adjust the score if he feels the IB provided an advantage to the OS (Law 27D).
Bottom line: call the TD, let him explain your options to you. If you think some action might be unethical, ask the TD. But I would say if he tells you one option is to bid 3
♦ (and he will), taking that option is almost certainly not unethical.