Well, they are definitely challenging at first, so don't feel like it's just you!
I might be wrong, but it sounds like you were rolling up the fatty itself, and the weave, at the same time. If so, that's one thing that's easy to fix.
You can prepare your weave ahead of time, assembling it on plastic wrap. Set it aside. Important: have extra bacon slices on hand to patch or complete your weave when it comes time to wrap the fatty. It's always good to buy an extra pakage of bacon. If you don't use it for fatty repair. you can use it for ABTs.
Usually the preferred bacon for the weave is the cheap, thin stuff. It's good if it's a little stretchy! I always pre-stretch my weave a little because I know it's barely going to contain the mammoth fatties I turn out. The first time I made a fatty weave it was with thick cut bacon from the butcher. It was what I had on hand and I didn't want to buy another pound when I had a pound already in the fridge. Big mistake! No stretch, so it was difficult to weave with and made a small weave, PLUS it doesn't cook through during the smoking process, so you end up with what looks like uncooked bacon wrapping your fatty.
Then when it comes to rolling up the fattie, try making your first ones with less rather than more filling. The temptation is to load them up. The more you put in there, the more difficult it is to roll up, and the greater the chance you'll have major leakage while it cooks. It's a good idea to leave an inch or so on both ends without filling so the sausage can stick to itself as you roll it up.
Also, it's a good idea to start with at least a pound and three-quarters of sausage, if not closer to two pounds. If you are rolling it out in a 1 gallon bag you can roll it out even a bit longer once you cut open the bag. You want a nice long stretch of sausage rolled out so when you roll it up the outermost layer is completely sealed. And it has to be sufficiently thick so that the filling doesn't poke through. I try to roll it so the interior end is thinner and the outside is thicker.
As you roll it up you have to sort of manage to tuck in the ends as you go. If your filling is immediately trying to get out, and there's no way to roll it up, take out some filling. Even if you only end up with half of what you wanted in there it's going to be incredibly delicious. Plus you'll feel more accomplished just getting one done with all the innards intact.
When you have the fatty rolled up and the edge and ends sealed, then you pick it up and sit it on one end of the weave. then you can use the plastic wrap to lift up the weave and drape it over the fatty. You can peel back the plastic wrap and tuck in the weave around the ends, and adding another strip if needed to cover a bare spot. I usually try to push the fatty over so the seam is under the fatty.
When the weave is in place, the whole shebang should now still be sitting on the plastic wrap. You can use the wrap to sort of squeeze the fattie into shape. I don't usually bother with this step. Once I have it in the weave and it's secure, I'm taking it to the smoker.
After you do a couple it gets a LOT easier, then you can start loading up the fillings! Just make it easy on yourself in the beginning!
BTW, and I hope I'm not wrong on this point, but I think 165 is the target temp for fatties.
I hope this helps!
Next time post the pix anyway! It's a lot easier to help if we can actually see what went wrong!