You'll get there!
I also use to take a long time to load a quilt, but after I stopped trying to do it the way some of the websites recommended, it started to get really easy and I can load a quilt in about 15 mn now. Often takes me way longer to select the backing than it does to load it.
1. don't worry about finding the middle, I like to keep my quilts toward one end so I can use the other for bobbin changes and cleaning, so I start on one and pin until I get to the other. It's taken a while to get a good feel so I don't stretch the backing as I'm pinning. I do pay attention so that the top and bottom are about the same, but I don't fret less than 1" difference (I'm mostly using 105" wide backing).
2. I roll up on to the back roll and then lay it over the front bar and have it hang over so the edge of the backing lines up with the edge of the leader. I pin so that it will "fold" over the pins when I roll and that does not matter. So it's more that I line up the two edges and pin like you'd do for a seam, but when I roll it opens up and the pinned seam lays to one side. This saves me a lot of time and has not caused any problems what so ever. I always rip off the selvage and rip across to have straight of grain. Even if it seems wonky, rolling it back and forth evens a lot out. Usually the first few rolls I'll have to make sure it's smooth and adjust the edges, but after a few I don't have to do that anymore.
3, I totally float my tops, and pin them to the backing as needed, and remove the pins as I'm stitching. The very first quilt I did - I "loaded" the top, and once was all it took and I've never done it since.
4. stretched a cord with movable locks (like those that helpe keep ties tight on a jacket) and them move those locks to help line up the edges as I advance - I use to measure and that was a lot more work. Now I just line up with the locks and it takes way less time.