Hey Figs, first of all don't worry about making what you think is a round loop. It won't be.
Never seen anyone come close to an actual round loop who hasn't had a good bit of help from the ground. Nobody does it on their own. Everyone pulls too softly to enter, and then VASTLY underestimates the amount of time required spent floating over the top around zero G with very little pitch rate. So just do what pleases you.
But still, a few basics - don't pull power off on the backside. I've seen a lot RV videos where guys pull the power to near idle on the backside for fear of overspeeding the airplane and/or engine. This is unnecessary and makes for a terrible loop even by recreational standards. RVs will easily loop from cruise power, cruise speed. 3-3.5G works fine for "L" shaped recreational loops, but not so much for actual round loops. So your G pull is fine for what you're doing. A loop is a symmetrical figure, and so should be your G loads up and down. They constantly change through the figure. Low on top, high on the bottom. On the backside, you just have to gradually increase your pull and accelerate the G load, feeling for about the same load on the bottom that you felt during the initial pull. You feel for the G acceleration rate that avoids stalling/buffeting on the backside, but is also sufficient to avoid finishing at a lower altitude than you started with. At a constant power setting, you'd have to break the laws of physics to finish a loop at the same altitude but with a higher airspeed. So forget pulling power off on the back. You can either set it and forget it, or add full power on the way up and return to your entry power setting on the backside. You just need to practice the acceleration rate on the backside to avoid stalling or finishing low. It's all done by feel. Sounds like you're just pulling too hard too soon on the backside. If you're pulling a lot power off, that makes matters worse.
Good question on the visual reference going up and over. I see lots of folks look straight ahead the whole time and then crane their neck back as far as possible trying to pick up the horizon on top. No need to contort and strain. This can also miss key information on the way up. If you have interest in flying with precision, I suggest an alternate technique on where to look and when - starting the loop, look straight ahead until you lose the horizon under the nose. Be sure you are perfectly wings level as you lose the horizon. Then glance to your left and notice the position of the wingtip relative to the horizon. You need to learn exactly where the horizon must bisect the wing in order for the airplane to be perfectly vertical in yaw as the airplane is vertical in pitch. Ground critiquing helps, but you can figure it out by yourself by flying some vertical uplines just long enough to glance left and right until you make the relative position of the horizon and wing the same on both sides. Once you've figured this out, every time you pull through vertical on a loop (or a vertical upline), you need to put the wingtip in this position. And once you've learned the sight picture, there is no need to bobble your head around looking left and right on the way up. I see lots of folks do that and there's no need. One wingtip tells you everything you need to know. This concept is fundamental to precision competition style flying should you want to get into that at some point.
So point being, if you get perfectly vertical in yaw on the way up, you will know the sight picture of the wingtip relative to the horizon such that you are automatically set up for a perfect wings level attitude by the time the horizon will come back into view over the nose over the top, and then you shift your view back over the nose for the rest of the loop without any neck craning. If you find that you must make rudder corrections to get the wingtip into this position, this means you made a slight inadvertent aileron input during the pull, which is causing an error. If you can pull to this perfect yaw attitude with no rudder corrections, you're pretty much set up for a perfect level attitude over the top if you just keep it going.
Well I guess I went overboard, but for me the little details are what make acro interesting and worth working on....at least for those of us who care to progress beyond "flopper" status.