I made my main character an assassin...my question is...what can i wear to make my armor class the same as mazzy (a fighter in my group) her armor class is negative 9, while mine is a pesky negative 1
That of course means i cannot fight at all without risk of getting the snot kicked outa me; which kinda sucks since im used to planescape torment type style where the rogue was the most powerful class (had highest armor class and could do the most damage)
I can barely hit stuff too
will i ever be able to get my weapon skill above just 1 star?

You can find +5 studded leather armour in the game, and rings, cloaks etc can lower your AC further. High Dex helps, try a potion, but a fighter can wear any armour in the game whilst a thief can only wear uo to studded leather. It will be difficult to equal Mazzy, without cheating. Sorry! Also thieves can never specialise in weapons, so you will remain at 1. If human, you could dual class to a fighter later. This would allow you higher proficiencies with weapons, but you would lose your thief skills, including backstab, if you wore armour heavier than studded leather.