Inconsistent betting patterns

Although I haven't been finding a ton of time for poker, I've been pretty diligent reviewing the sessions that I so play.  I've noticed that I still have a tendency to under-size my bets, especially on the later streets.  Betting too little can be just as bad as calling too loosely; either way, your bottom line suffers.  The insidious part about betting too little is that it's a little more hidden.  Your stats don't get affected enough to notice, so you really have to dig through hands to figure out that you bet too little, or have someone review you.

The strange thing is that as I'm reviewing sessions, most of the time, my bet sizes seem pretty good, but then for no apparent reason, I'll have some small bets scattered in the session.  I'm trying to figure out what makes me inconsistent, as well as what just makes me bet small in the first place. 

My gut reaction is that I'm playing with a little too much fear.  I'm rolled well and table select well enough to feel like I have an edge when I sit, so it's not those things that would be scaring me.  It might be that I'm afraid to make a big mistake.  Not that I like it, but I don't really mind terribly getting stacked when it's a clear cooler or beat, but I hate the thought that I could be making a big mistake.  I want to be good enough to not make big mistakes. 

For instance, I played a hand recently where I ended up stacking off KK.  I raised UTG and TAG calls in SB.  Flop was Q22dd that he c/c.  Turn was an offsuit 9 that he c/r.  He shoved river which was an offsuit 4. 

Of course he could have a boat, but if he's at  all capable of overplaying AQ or bluffing JdTd, then it's going to be close one way or the other.  The feeling I had when he showed QQ was quite disproportionate to the mistake I made.

Hopefully, writing about it will reinforce my focus on making more confident bets and realizing more value.