Short answer: Probably not worth it.
In general, while the aura has some interesting effects, it costs too much to activate, probably.
Necrotic resistance and +1 AC are pretty decent, and the curse is ... well, it's okay. But since your existing blade does better damage already (is your existing blade +1?), all that leaves is being able to stop attackers from finding you when you hide.
The ability to change the damage type of sneak damage is pretty nearly irrelevant. The weapon is magical, so it already overcomes most sources of resistance or immunity to stabby damage. So unless the target is vulnerable to poison/necrotic (very rare), or resists magical stabby damage but not poison/necrotic (also very rare), I don't see much point to that.
Here's what I'd suggest:
Rogues benefit from dual-wield. Use your existing fire dagger as your main-hand weapon. If you hit with it and deal sneak damage, great. If you miss, you can spend your bonus action to attack with Scarlet and try to get your sneak damage anyway. Just use it as a +1 dagger.
Once in a blue moon, maybe you get into a bad spot and do the blood aura thing to try to improve your chances of escape, but most likely you never use the dagger's full potential.
But:
The imbue vs cast thing isn't very clear (I assume the DM meant them to be synonymous), and it doesn't say when the damage can be healed. Does the DM mean it can't be healed while the aura lasts? Because that's not so bad, you can get cured after the fight is over. If it really is for the rest of the day or something, then no, I'd never use the dagger's blood power.
Talk to your DM about your concerns.
If he gave you a 'cool artifact' weapon, he obviously expects you to use it, and if you feel it's too much of a risk to ever use, he may be willing to work with you on it. See if he'd be willing to cut down the aura's cost a bit, like make it a d6 damage so it's a little less risky to a squishy rogue. Or have the aura give you resistance to all damage instead of just necrotic, so you're taking damage now in hopes of taking less damage later.
Just some ideas.
At least by the rules as they are written the dueling bonus applies to both attacks. On page 24 of the SRD the Dueling Fighting Style text is:
When you are wielding a melee weapon in one hand and, no other weapons
you gain a +2 bonus to damage rolls with that weapon.
Note that the bonus to damage is activated immediately. So, if you lose one of your psychic blades and immediately gain another you get that bonus applied.
Best Answer
First and foremost: If you haven't read this, stop now, go read it.
Second, L3 is kind of a lousy level for Roguish armor. L4 has some good choices (Bloodcut, Battle Harness, Flowform). But if you've got to pick from the L3 lists let's see what we've got: (not hitting everything, I'll hit your two and a few more that are good)
Bestial: nice if you charge, but if you don't then it's not worth the paper it's printed on.
Nightmare Ward: incredibly situational, you can't afford that, find stuff that aids your core goals. Unless you've got a campaign situation that merits this.
Sylvan: bonuses to Athletics and stealth are nice. Mostly just stealth.
Serpent Skin: Nice daily shift that's very handy. You're already pretty shifty, this enhances that.
Skald's: +2 bluff, Diplomacy. Daily to retarget an attack against you (including to an enemy).
Thought Eater: +2 Stealth. Daily to get concealment
Veteran's Armor: Attack bonus is one of the most important things in 4E, and this helps with it.
Not many good options here. I'd suggest the serpent skin or skald's (probably the Skald's armor is the best one at the level).