i printed some pdf sheet music online, then i punched 3 holes in the pages and put them in a binder.

some problems:

the sheet music droops to one side. is there a way to bind sheet music that is cheap (3 ring binder + 3 hole punch is cheap) and also allows you to easily add in more sheet music later (3 hole binder). i was looking at some binding options at staples, most were not cheap nor would you be able to easily add more pages later when needed. so what options do i have? and how do you organize your sheet music? and is it necessary to bind the sheet music?

I've had this problem with 3-ring binders too, so I got myself a 4-ring one, which minimises the page droop.
But mostly I use display books like this one:display book.
Reflection from the plastic pages can be a problem, but it works for me in most circumstances. I don't know whether these are available where you are, but you can certainly add extra pages easily.

That is very cool! I've been gluing pages to black folders for performance pieces she practices over and over. It's durable without glare but I thought there had to be a better option.

It sounds like you printed it on ordinary cheap paper. Try using some heavier paper. It isn't expensive and something like card stock would never sag. An ordinary printer can print on thicker paper, that won't be a problem.

It might help somewhat to print your music on a stiffer paper. If you bind your pages in covers which are the same dimensions as the paper, there will be nothing for them to droop over. You could even cut down the edges, if it comes to that.

it is not the paper, it is thick and stiff enough, it is the three holes that is the problem. try it for yourself to see what i mean.

I have my piano music, trombone music, handbell music, and voice choir music in 3 ring binders. (different ones, of course) I've never noticed the droop problem, but I do use the punch with the big holes. Maybe that makes a difference. For sure stiff paper makes a difference.

I also have some I bound with that plastic edge binder like you see at Staples. That is much nicer. It's pretty easy to add pages, the same machine that binds them pries apare that plastic clip thingie.

Years ago a fellow trombone player came up with an idea to make his marching band music indestructable. It is a bit complicated but he raved about it. He scanned the music, converted it to mirror image, and printed it on the back of a transparency sheet. Then he glued poster stock under that, so the print was sandwiched between the transparency sheet (like for the old overhead projectors) and the poster stock (like for yard sales signs). He could definitely play in the rain! and the transparency didn't glare in the sun quite as bad as a sheet protector, but it could still be a problem on a real bright day.

If you shop for sheet protectors, be sure to get the kind marked "non-glare". These work. They do not have glare that you get with regular sheet protectors.

I print double sided on stiff paper (100g). Then I get them comb bound at Staples. Works well.

I was also going to suggest sheet protectors. I have my music in thick binders and use the non-glare, better quality sheet protectors with no problem.

If you are using sheet protectors and regular paper is too floppy you can slip a blank piece of card stock behind your music. It is not necessary to copy on to the cardstock.

I tape the individual sheets together side-by-side (so when you open everything up it makes one long line), and fold it accordion style (so it opens up like a book). Then I hole-punch the left side and put it in a binder.

This works great and it's not floppy at all.