Well, I looked up your lolking, so I guess I'll start with some runes/masteries advice.
Typically people format 21 mastery points into one category for the top tier bonus, and 9 into another. Ahri is almost always either 21/9/0 or 21/0/9. Rune wise, you probably should build up the two standard AP and AD pages, and then you can leave them alone until you're satisified with your champion pool. Those pages are:
9 armor seals
9 MR glyphs (flat or scaling, I like 3 flat 6 scaling)
9 mpen marks OR 9 AD marks
3 AP quints OR 3 AD/AS quints
They'll work reasonably well on any champion.
I also see you're taking heal every match. Ignite is preffered on aggressive champions, especially midlane where your opponent will probably also have ignite which counters heal.
Anyways, I wouldn't worry about getting people's hopes up. Champion mastery means no more than what it means for you: that someone has played the champion a lot. But players don't improve unless they try, so.
CSing. It comes with experience at the game naturally. You usually want to avoid letting your wave fall under the tower because its harder to get the last hits. If the wave falls under the tower, the basic last hit guide is that a melee minion takes 2 tower hits, then 1 auto from you. Ranged minions need 2 autos from you, and 1 tower hit, so you have to hit them before the tower does once, then again after. In Ahri's case she's a champion with waveclear, and she'll often blow the wave up if it gets pushed towards her tower. If you have to take some minion damage getting the last hits, that's okay.
For a standardized Ahri core build, you're looking at something like 
. I really find Luden's Echo is the item that powers her up best, while Morello's fits your needs. But she's pretty good with most items and its worth staying flexible, particularly based on laning opponent. Don't mind going 
against, say, Katarina.
The easy way to hit charm is to just be patient with it. You can sling your Q if you want to poke, but charm is best held onto until things get going. The whole "land charm and burst" thing is really not necessary. You don't need it to hit your other skills, and its not her burst that makes Ahri unique. Its staying on the fringe and sides of a fight and firing into it, while baiting and charming opponents out of position.
