Am I being too nice or just getting used?

I’m a 23M attending my cousin’s wedding and I’ve been helping with almost everything they ask even small things like washing the car and running errands. On the wedding day I basically worked nonstop while they were on stage.

Part of why I don’t mind helping is because my Dad often stays at their house when my dad comes here for medical treatment, so I feel like I’m repaying that kindness.

But I’ve started feeling like I might be an easy target. Some other cousins refuse to do certain tasks and no one pressures them, but I’m the one who gets asked or even scolded.

Another thing that probably made this dynamic worse is that my dad has scolded or even verbally abused me in front of my cousin brother's parents before, which may have given them the impression that it's okay to treat me that way too.

Now I’m wondering if I’m just being kind, or if I’m losing my self-respect by not setting boundaries.

Would appreciate your thoughts. Please be kind.