First, going by the information in the wiki, your calculations are off. At level 6, landing a single Q will deal 140 + 75% AP. With 100 AP, that is 215 damage. This is assuming that Syndra is maxing it first, which would mean that it is at rank 3.
At level 6, her ultimate deals 90 + 20% AP per sphere, and with one Q out, that will be 4 spheres. With 100 AP, that's 110 damage per sphere, or 440 damage overall. Add that to her Q damage and you get a total of 655 damage, not 735.
Secondly, you're talking about RAW damage. All of this damage calculation is not taking into account the target's MR. All champions start with at least 30 base MR, some a little bit more. With 30 MR, all magic damage dealt to you is reduced by around 23%. 23% of 655 is about 150, so you would take about 150 less damage, or 505 total damage from a single Q and R. So that's about 230 less damage than what you originally thought.
Of course, this is assuming that your target does not have any extra MR from their runes/masteries and that they haven't bought any MR items, which would reduce the damage even more. If Syndra has 100 AP, then she has bought 1 or 2 items for that, meaning her lane opponent could easily have bought an MR item.
EDIT: Next time you want to complain about a champion that you just lost to, try to do it better. There are many important factors that you are leaving out in your argument.
