Slide - FWIW, I'm in pretty much the same situation as you - you are not alone

I am trying a sneaky mage/thief, and have found that the flame spell (and yes, it took me a long time to figure out how to cast it - i'm new to the series) does very little damage - I can barely kill one enemy, usually.
So my not-very-successful tactic so far has been
a) shoot an arrow, maybe two, from a distance. some damage is better than none, and the fire spell doesn't range as far, and maybe someday my bow skill will increase.

have flame in left hand, heal spell in right, and flame away
c) if it looks like i'm about to die, either quaff some healing potions, or run away.
this got me (barely) through the initial dungeon (barrow's temple, i think it's called?), and I'm now L4, but like you I feel like I should be doing a lot better.
We shall overcome!

PS and the reason i'm not using other spells is because i haven't been able to afford them yet. Something that would either work at range, or slow enemies, would be fantabulous.