I will suggest what is probably an unpopular choice on the board, but I think it might help to find a professional that you can trust or even a good relative to help you relax it all.
It might be a big task to do your whole head, especially when you're not used to dealing with those type of chemicals.
But if you do it yourself, my biggest mode of response would be to do your hair in sections and take your time. Who cares if it takes a long time, it's your hair. When I relax my own head, it probably takes me 5 hours, lol! That's a long time but it comes out the way I want and it's free, so to me that's what is most important.