hope everything goes well for your dress rehearsal. do your parents have a video camera? you can sort of improve yourself from the dress rehearsal, even, with a little video and refine your 'look.' how you walk out, how you present yourself, and things that you notice about how they take the music, what the conductor says, timing, etc.
something that your family may already be aware of , but maybe something to remind them of is to be extra quiet on thursday. it would be very distracting for me to try to carry on small talk or be asked too many questions instead of focus ont he music before or in-transit.
be ready for unexpected questions about saint-saens concerto from the audience afterwards when they come to congratulate you. 'when was that written?' 'how do you pronounce his name?' things like that. it's funny - but sometimes you think you know a piece and then someone asks a quesiton about it and you have to think. the bolder the better. when you walk to the piano, make it like you are walking to the bathroom when you gotta go. not a promenade looking at the audience. (sorry to be so silly this morning) - but seriously, people take note of you the moment you walk in - so you have to be purposeful. you sound like you already are.
something that works for guys as well as girls are square-toed shoes, too. (and make them shiny). they cover the pedal well and make your pedalling less of a nuisance. remember not to lift your foot completely - but just find that 'pedal-point' and practice 'hovering' around that point. extraneous noises take away from the sound. oh, and don't forget that ever famous handkerchief. you can't be a 'case study' unless you can pull it discretely from your sleeve and wipe your forehead in between the last moment you played and the cadenza. it just gives a good effect. (and, if you want to be really magical about things...put a drop of water on your head and keep your head level until you get tot he cadenza. while you play the cadenza, let the drop roll down your nose and make people think you are working terribly hard). it's all in the show, ok. well, mostly the music - but some of the show.