I'm a day late, but it seems that nobody has answered your question. Here are some things you could have done differently:

- Have a vesting schedule for your equity. This way if things go south, you'll have a certain portion of your equity vested. - Negotiate a higher equity stake in the first place if you're playing such a founding role. In my opinion, if the product didn't exist before you joined the team, then you're a founder. Remember that we're looking at this with the benefit of hindsight. - Made the agreement up front that you had control over the technical decisions since you have the expertise to make those decisions.