There isn't much of a difference between Standard and Advanced. Firstly, they share the same area of study. On top of that, the method for learning each module is almost exactly the same, you go through the rubric, do a few boring sheets to aid with your understanding, read and analyse your text then write an essay. The only difference being that the modules in advanced and standard differ slightly in terms of their level of sophistication and books.
You have almost the exact same workload in standard, in my school, they put everyone who dropped from advanced to standard in the same class, some were even highly encouraged to drop or were "forced to", most of them have lost all motivation and the class is half dead. The only realistic difference for standard and advanced is the level of competition and ultimately scaling, unless you are coming under the top 70% mark, you shouldn't drop. The main reason teachers urge you the drop is the keep you from dragging the other students down. But if you stand up and properly practice writing out essays and the occasional comprehension, you would keep up.
Even if you REALLY are struggling and drop to standard, you also have to keep in mind that there are many people who are really good at English but chose to do standard, you would have a slightly higher rank but you would get scaled down. In the very end, the only thing you can do is to do your best and not end up regretting not working hard enough. Maybe make is a goal to write an essay and hand it in to be marked once every month, your teachers will be more than happy to help mark an essay by seeing someone who is just average make a major effort to improve their studies. Good luck, I hope this helps.