You can’t go back in time and change the terms. Even if this was in writing as a signed contract (which it always should be) according to the terms you stated you would be entitled to nothing.
Thing one) hire a lawyer to write up a standard contract that you can easily modify terms on.
Thing two) when doing a royalty agreement, make sure you get what you need out of it (IE, if you don’t really need the money, make sure you get the rights to show the work, make sure the royalties have a guaranteed minimum for year one, or a design fee to cover your butt and at least get something, or a design fee in the form of an advance on royalties that serves as a minimum.)
Thing three) always have a paper trail. Email trains, signed documents, all that stuff is necessary if you want to have any real legal recourse.
Thing four) don’t be afraid to be annoying. Call him up and try to get some compensation. The worst he can say he screw off and you are no worse off than you are now. Likely he will say “I let more than you” yada yada yada, at which point I’d tell him since there is no agreement, you technically own the IP and you will be making the work public… something like that.