There's two problems I have with this game:
1) This is easier than most of the cash games on the show. The easiest ones is 1/2 Off (if my math was right, it's 11.7%), followed by Grand Game, which has 6.67% chance of winning. The setup you have has an 8.33% chance of winning [(1/2)*(1/2)*(1/3)], plus it has a guaranteed higher payout than both.
2) You're essentially playing a 3-prize version of Plinko's SP portion. And while Plinko has a 2nd part of the game, yours doesn't.
If you were playing for a cash prize under $10,000, then I'd say the game is pretty good. However, it just seems way too easy to be a high-payout cash game.
The only suggestion I can think of is to have each of the 7 (or even 6) prizes a choice for each digit, and make the contestant choose 3 out of the 6 or 7 to use as their "digits." You can even have it so that one of the digits will work for 2 of the SPs, if you wanted to make it easier. Assuming you're using 6 prizes and you have 2 SPs that can work for one of the digits, your odds become: (2/6)*(1/5)*(1/4). That's about 1.67% chance of winning (0.83% if you have each SP require a different digit), which makes it on-par with high-payout games.
For some reason, when I read this, I thought of a gag that Drew could do. The "carbon copy" price could have some kind of obstruction over the first 3 digits that purposefully make it unreadable (i.e. a coffee spill, an ink blot, a lipstick mark, toner ran out, etc) and the contestant has to "make a new one." The obstructions would be something that you'd expect to find in an office.
Here's how I imagined it:
Drew: "Congrats Dan, you've made it on stage for a chance to win a certificate for $14,200 in cash playing Carbon Copy. Here's the original right here. And guess what: you don't have to do anything! We've already made yours: take a look, it's behind this cover!"
*cover reveals the carbon copy, but a huge coffee stain is obscuring the 3 numbers*
Drew: Amber, what in the world happened?? You ruined it!
Amber: I'm sorry, Drew, today was a mess! I overslept, my car got a flat tire, and I missed rehearsal! I must've spilled my coffee on it while I was running to my dressing room...please forgive me!
Drew: Did you remember to feed your cat, though?
Amber: *gasp* Oh no, Mittens! *runs off stage*
*audience laughter/applause*
Drew: Well, there goes Amber. Well Dan, I guess we'll have to re-make your copy. But we can do it with the help of these small prizes...
*cue rest of the game*
BTW, I don't even know if she has a cat. I'm just giving an example of the kind of humor they could have in this game.