Oï mate.
I’d say that you went wrong on quite some points 
First of all : using laser ships against Guristas or Serpentis is not the best idea, because the resistance pattern on those ships make it hard for EM damage to deal good damage. You should try to find Agent missions in Amarr space, against Sansha Nation or Blood Raider, where you’ll already deal better damage. Even more, both those rats deal EM/Therm damage, which is what Armor is already good at tanking without modules, so you will take even less damage.
Then, you made one of the worst possible mistake in EVE Online fitting : dual tanking. A shield module has nothing to do on a Maller ! Drop that Adaptive Invulnerability Field I to either put a cap battery, for some cap stability and resistance against Neutralizer, or a Tracking Computer, for better tracking against smaller targets and improved range.
With a better range on your guns, I’d say you can take some Standard focusing crystals, as they’ll gave you some range to engage targets that aren’t in the optimal range of the Ultraviolet. Some Radio crystals wouldn’t be too much, to do early DPS if the rats spawn far away from the warping point. The best thing you can do to improve your damage without waiting for your skills to go up is to invest in some Imperial Navy Crystals, they aren’t that expensive and it’s one of the best investment you can make to get your DPS up.
Another thing you can do is get rid of the oversized afterburner. The 10MN ones will get you some good speed to reach your destination faster with subwarp engines, and will be less heavy on your capacitor. Your best bet would be the ‘Monopropellant’ version, since it have a reduced capacitor consumption.
Finally, for a better tank you should try to squeeze in a medium armor repairer, since armor doesn’t have a passive regeneration, it’s your best option to do a site in one go. Replacing the plates will give you less buffer, but an improved agility and speed. Also, replace your T1 EANM with ‘Prototype’ versions, or any Meta module of your liking, since they give better bonuses, cost less in terms of CPU and powergrid and are dirt cheap.
There, you should be good. The Maller is the Amarr tanking beast of the cruiser line, with a somewhat good damage with its turret because of the +5% bonus to energy turret damage and 4% to armor resistance per level of the Amarr Cruiser skill. However, you could also take a look at the Omen, which is less tanky, but have a capacitor use bonus, which should help you if your Engineering skills aren’t high enough to support a tank plus your guns. There is the Arbitrator too, that make for a good droneboat, and can technically reduce the incoming DPS by using Tracking Disruptor, but it have a limited use against NPC.
Also, note that the Maller make for a better brawling ship with Pulse lasers instead of beams because of the superior tank when compared to the other T1 Amarr cruiser, while the Omen is more suited for range combat. But hey, it’s EVE Online ! There’s not a single way to fit your ship, so don’t trust the retards in the Amarr NPC Corp chat that tell you to get a Gila or calling you dumb if you don’t :3