YANBU - it is entirely unfair when a parent favours one child over another and it is completely reasonable to feel hurt and a bit miffed by it. My mother favours my brother, which i find hurtful but i just get on with it now. (He was invited to my dad's surprise 60th birthday, i was not. When my mum won money to go on a 5 star holiday (£20000) she took my brother, his girlfriend, his best friend and his best friend's wife, my aunt and not me; when my dad was dying she sent me home from his death bed and told me she would call if anything happened and didn't phone until after he had died with her and my brother by his side.)
I'd ask but be prepared for any answer.