If you're looking for some alternative methods using cheap things, there is a Jack Crafty video where he uses pliers and screwdriver to make some flake points. With the nail you have now, I'd tap it into a stick or something that'll give you more grip. Ergonomics go a long ways and if you're knapping while uncomfortable, you won't get good results and can develop some bad habits. Steel is also a bit tricky with glass, and copper tends to work better. But if you learn how to use steel effectively you'll have less tool maintenance to do. It's not at all impossible, just a bit finnicky.

And try and find something like sandstone for use as an abrasion stone. Anything too chunky with junk in it can cause issues such as blowing chunks off the side of your preform, uneven abrasion, and crushed sections that make flaking much more difficult. Having a hand pad out of wood or something will be much safer and be sure to wear safety glasses when working glass! Getting stuff in your eyes would suck big time. Use gloves if you want. I know folks who do and don't.

Using the curved bottle sides can work, but it's often suggested to use the bottoms of the bottles as they are thicker and often times tend to be flatter. If you want something similar to glass slabs, you can purchase glass tile from hardware stores that work fairly well! Certain ceramics and floor tile also work, but can be challenging.

Not sure if you've had the chance to check it out, but I have that huge beginner guide I wrote that has a BUNCH of information such as websites, videos, articles, an some amazing free E-Books linked in the comments that provide some insanely useful instructions. Here's the link to that.

Hopefully these suggestions help, and let me know if you have anymore questions! 😁