Help, please

For nearly 4 full weeks, I have flailed and struggled to optimize my DPS for the sake of my friends while we run Mythic+. I know that Necrolord’s isn’t an ideal choice of a covenant for PvE and I know I’m not a very seasoned player, all things considered, but I’ve been trying my damndest to make it work and it’s simply never good enough.

As a subtlety rogue player, I am reaching out and pleading for any sort of assistance. For starters, please tell me what’s wrong with my rotation (and I’ll include my talents above the rotation).

15: Premeditation
25: Shadow Focus
30: Deeper Strategem
35: Soothing Darkness
40: Prey on the Weak
45: Enveloping Shadows
50: Secret Technique

Now, for the rotation:

Start in Stealth
Shadowstrike
Bone Spike (Coven Ability)
Shadow Blades + Shadow Dance + Symbols of Death
Shadowstrike
Shadowstrike
Rupture
Shadowstrike
Shadowstrike
Slice & Dice (since this is nearly the 10 second mark from the initial premeditation s&d)
Shadowstrike
Shadowstrike
Eviscerate

Repeat the eviscerate cycle while maintaining slice & dice and rupture on target. Use Shuriken Storm when adds are involved to eviscerate. Pop Vanish for additional Shadowstrike, and pop CD’s when available.

What am I doing wrong? I can never compete in DPS and tanks almost always out DPS me. I’m… frustrated and very close to giving up on the class.