None, really. You're kicking ass. For a first-timer, your RP skills are excellent, awarding you bonus XP at every turn.
A little to improve on, here.
A dagger does 1d4 damage against medium and small creatures, and 1d3 against larges. Even with Sneak Attack, that's miniscule. A shortsword is far better (1d6 SM, 1d8 L). However, it is unfortunate that once you backstab someone you are painfully open to being attacked. At 12 gp and one bolt per round, the light crossbow is the perfect substitute. The damage is someone lacking, at 1d4 against everybody. A heavy crossbow is 20 gold, but it takes a turn to reload it, so it's 1d4+1 against smalls and mediums and 1d6+1 against larges really averages out to about 1 DPR with a heavy, 2 DPR with a light. The less cost effective way is to either buy darts (which are 1d3 SM, 1d2 L, BUT can be thrown 3 per round for a DPR of about 4 or 5), or daggers, which are bought and used like normal daggers but can be thrown 2 per round for the above damage (1d4 SM, 1d3 L, for a DPR of about 4, but which adds the versatility of also having a ready supply of melee weapons, while sacrificing range).
Really, none of these choices are perfect. If any, I would exclude daggers if your not going to throw them and the heavy crossbow for the sake of speed, but besides that your DPR is going to remain in between 3 and 5 against small or medium creatures, which is really 6-10 DPR because of your sneak attacks, which is respectable considering the average DPR the rest of the party is doing varies from 2 to 6.