As Bront may have eluded to, there is alot of mystery in your mech. I, for one, am curious about its engine size, armor dispersion, heat sink type, ect; if you have time, and you are interested in more fine-tuned feedback on your built, I suggest using this site:
http://mwo.smurfy-net.de/mechlab#i=17. There, you can build your mech, and use the "Share & save loadout" command towards the top of the screen. It will spit out a few links; post the plain link in the thread, and it will provide access to your mechs' schematic. In anycase, same as Bront: if you are not using double heat sinks, I suggest you purchase them. Unfortunately, the way the game is, they are far too advantageous. Other than that, I think your built is fine for close combat brawling. That's an intrinsically difficult role to fill at the moment, but, I think you have appropriate tools to fill it; in terms of weapon systems. Though, like Bront mentioned, don't put too much stock in the firepower rating. While it should be in the 60ish range I think for a Atlas brawler, the number is only really relevant next to heat efficiency; due to the importance of DPS for the role. Shutting down within 300m of the enemy is far too risky. Though, as you're a new payer; his advice of restructuring your mech as a more ranged combatant may make the learning curve easier. If that's what you end up doing, I definitely suggest dropping the AC-20 for the Gauss Rile.
As for other advice, I think you may want to consider embracing the "big sister" role. Whether I'm piloting my brawler AS7-D, my sniper AS7-K, or my more balanced AS7-D-DC; I find the mech shines when I use it to take care of my "sibling" mechs. Whether that means being the spear-head of an assault, an ECM shield, or fire support/missile watch-tower. The Atlas, or most assault mechs, are especially connected to the team formation. This is due to their speed, large profiles, increased likelihood of being targeted, ect. The schoolyard bully analogy makes me wonder if you're primarily flying solo. If that's the case, then I think apart of your learning curve should be trying to find your place in the team formation. A good Atlas pilot in the middle of a firefight can have an especially disproportionate influence on the entire flow of proceedings; though not without supporting, and being supported by, the other mech's in that situation. If you go it alone, you may find yourself dying like a legged jenner; 100 tons or not, 66 firepower rating or not.
In anycase, I hope that helps.