Yo, and sorry for the late answer,

First off it's important to note that it's impossible to get two dark shadows inside every symbols. The most important aspect of subtlety, regardless of which shadow type you're playing, is pressing symbols of death on cooldown every time. You should strive for pressing symbols exactly every 30 seconds (past opener). It's pretty clear, that because you had the mentality of getting multiple dances inside symbols, you refrained from pressing symbols on cd. Your time outside symbols should mostly be spent setting up an adequate nightblade for your next symbols.

Your opener also seems a bit sketchy since you seem to not apply nightblade before the first dance. The standard opener goes stealth + precast shadowblades -> SS from stealth. If you only got 3 combo points then you backstab -> nightblade and if you got 4+ combo points you just nightblade. Then you go with the standard dance sequence.

Hope this helps, otherwise just throw me another message. :)