No it isn't, this appear rude because ~Quiero~ is the imperative(we use imperative for give orders like ''RUN!'' that in spanish is ''Corre") form of the verb ~Querer~.
So if you want to be more polite you will say ~Quisiera~ instead of ~Querer~.
So you will ordening like this "Quisiera.......(the food or thing that you want), por favor"
For sum up, use ''Quisiera'' instead of ''Quiero'' to appear more polite.