Welcome to HBT!!! I usually added 20-33% of my extract for the start of the boil, and the rest at 10-15 minutes. Do a search for "late extract addition" or something like that, you'll find ways to do it, and other information.
Also, I would get rid of your 45 minute addition. I'd put them into the 75 minutes, and put the rest at 15, 10, 5, and flameout (or something like that). You'll only be getting the bitterness from the 45, just as you would from the 75. By having late hop additions (and lots of them) you'll get lots and lots of hop flavor and aroma (which I'm guessing you'll want from and IPA).