Only from personal experiences can I say that I do have to disagree with tisha on this one 
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She is correct that most of the times that a girl will tell you that you’re just friends, then you’re just friends. It really is one of two things, you’ve already relegated yourself to the friend behaviours, you didn’t keep sexual tension between you two and kept the light flirting up. The more I experience the more I start to realize that it is very very hard to keep a platonic relationship with a female or vice versa for them. There will always be an inkling of attraction or tension between the two. Now whether the people act on it is a different story.
A majority of my experiences of hookups and intimate encounters have been with friends. I can tell you that if you handle it with care and maturity that you can continue being friends. The only thing is to be up front about it.
Let me break down the “game” for you as easy as possible. The behaviors and actions that the books teach you are essentially all the same thing, yea they throw lines in and steps, but it just comes down to these things; comfort and confidence. You have to be comfortable with yourself and your surroundings that your body language has to show it, the more tense you are the more you will exude that and on the people that you’re trying to “game”. This directly leads to your confidence, this is really the main aspect of what you need. And confidence, either through validation (will elaborate on this in a little bit) or continuous self improvement will help get you out of the friend zone. I’ll go over game basics, on how I’ve used it, then go into how you can use that to give yourself a better chance with her.
When you’re secure with yourself, you exude the confidence, that “walk”, and that aura that women just absolutely find instantly attractive. You essentially will have to take what is stopping you from being that and then work on overcoming them. As you overcome them, your confidence and comfort will go up. Women will be able to tell that you’re comfortable in your own skin, you’re in your element. You have to change your elements around so that no matter where you go, you will eventually lead up to being comfortable anywhere you are whether you’re in a club, a bar, a dinner, a date, or at the grocery store. You’ll be able to talk to women so naturally that your attractiveness will instinctually come.
The biggest mistake the guys make when trying to do this with a friend is use techniques and moves that are so off what they’re used to you that they will think its a farse and just dismiss it, some will even get completely turned off by it.
I’m just going to link you to my writeup on this before, that should help. There may be some inconsistencies because I wrote that a few months ago and I’ve been continually improving myself and the game that perspectives could have changed. If you have questions, just ask.
As for pheromone usage, I personally like A314, but based on your age on the page and her perceived age compared to yours, I would go with Instant Gentleman. Get some IH in there and Instant Shine. A low dose of TUTH later on as you escalate flirting and kino would definitely help you out. Remember that you have to do this SLOWLY and do this on your own terms, and don’t be an ass, if she texts you, respond. It may not be on the spot but you have to respond sometime that day. When you do talk to her just explain to her that you really did mean to get back to her, but because of what was going on, you were always getting sidetracked, it wasn’t your intention to ignore her. That’s it, people will only chase so far.