Did I rush into building this too fast?

I started working on a small delivery app idea after seeing how many local shops still take orders on WhatsApp. A friend suggested I look into flutter app development services since it could work on both Android and iOS without doubling the cost. Now I am stuck wondering if I should invest in development or first validate demand properly. Has anyone here built an app and realized later the market was not really there? Would love some honest advice before I move ahead.