I was reading my way through this before I posted so you answered before I got to typing... - yes, the spool was too small for the job..... My anchor line for my boat is 250' (and I have a spare 100' stored) for typical 100' depths......
In any situation like this, if one end of the line is anchored and the other is flowing in the current, there will be a significant slope to the line. If both are flowing in current, though, it will be quite different.
On the last dive I did, there was a very long line attached to the wreck in heavy current, and it was significantly sloped. As we left the wreck, we untied and the line went slack. By the time we were doing our deco stops, we were just hovering nearby and watching the line hang straight down as we all drifted along in the current.
Similarly, if shooting a bag from a wreck in current, you have two choices, depending upon how much line you have. You can start your ascent and then shoot the bag, or if you have enough line you can shoot the bag and
immediately get off the wreck and start the drifting ascent. Either way, you will soon have a vertical line. During a safety stop you can watch the spool or reel dangle in front of you.
Of course, the problem with that in this scenario is that your boat is moored and cannot follow you until everyone else is on board. They will need to keep an eye on you as you drift, and if you drift too long, it could be a problem. That is why it is something to be avoided. If you ever have to do this, you should therefore shoot the bag as soon as possible so it comes up close to the boat.
Your better choice is to make good decisions about your gas management in the first place so that you can get back to the ascent line without getting into this mess.