You're doing fine. NL ring games live tend to be a better cash cow than limit games for a variety of reasons, The most of which are:
1) In NL games you'll get fewer callers for your raises, making your big hands worth more. AA loses VALUE tremendously in a 3/6 Limit game when in most hands you have between 6-9 preflop callers in the hand. Even to a raise.
2) Position means A LOT less in limit. Tied in from the last example, lets say you're dealt KK on the button. And there are 5 limpers to you. You put in a raise on the button, the small blind folds. The big blind will almost certainly call you, as will the other limpers - it only costs them 3 more dollars to call - and they're not in trouble of loosing their entire stacks at once, wheras in NL, if it limps around to you on the button with KK, a raise to 15 straight will usually knock out any low holdings such as connectors, or suited kings or queens while the only ones staying around for 15 would be 2 face cards, or a high ace. (a-10 or better)
as an aside for a moment, the low-limit players aren't much worse than the NL players at a B&M casino, but in general most of hte people you'll play aren't very good. These people will see a hand for a flop a vast majority of the time with any pair, any suited card, any connector, any face/junk and any ace (more so at limit than NL because the raises knock these hands out). The players at 3/6 usually will "play sheriff" to assure themselves you're not trying to steal the pot. Which brings me to #3.
3) 3/6 limit is generally impossible to bluff, and the semi-bluff weakens in power. For example, you hold 67s in the hole, and you hit a pair, and you have had good reads on your opponent all night, and you put him on a set of trips on the turn. However, you have a redraw to a straight AND the board is flushing, but not of your suit. Playing against a good player (or in NL where the bets can really scare someone off), you're likely to win 2 ways (assuming the board pairing gives him a higher boat). The straight card hits giving you the stronger hand, and taking him for the most money you can get out of him, or the flush card hits and you bet him out of the pot. The turn play plays alot into this. Lets assume that hte 2nd flush card hits on the turn (which also gives you the straight draw). You put your over-sized bet in, indicating you're on the draw, and when the scare card hits, your opponent has to think twice about calling the big bet you make on the river, and very often will throw away his trips. (its not a good example, but go with me here.) In Limit, your turn bet will be 6$. Always, and the set will call you. Then the flush card comes on the river, giving you nothing. If you bet again, you'll be called because its 1 bet, and its worth the call. Long story short, you cannot push anyone off of a hand. Which leads to my 4th point...
4) Drawouts are all too common. I was sitting next to a guy (on the right) who would play ANY TWO CARDS every time for 3 dollars, and if he'd already put in 3 dollars and there was a raise he'd call a raise EVERY TIME. "Any two cards can hit a flop" he'd say. Well, i played my usual tight aggressive, and played only the strong hands Any PP, AK-AT KQ-KJ and QJ, and suited connectors. This guy seemed to be taking down pots left and right with crap cards, and one time cracked my 2 pair AK with a 2-6 when he hit runner runner 45. (A3K45). This is MUCH more common in limit.
So, in general, if you can play NL well enough, DEFINATELY stick to it. The bad beats are rarer, and the money is better. The same players play 1/2 NL and 3/6 limit - so capitalize on their mistakes when it costs them 100$ rather than when it'll cost them at most 18$.