I'm new here! Hello

I'm into my strong IPA's in a big way. I really like Brewdog Punk IPA which stands at 5.6% and an IBU of 45. I also like their Hardcore IPA which stands at 9.2% and an IBU of 150.
I recent made a basic IPA kit, but it only worked out at 3.5% and wasnt nearly hoppy enough for my tastes. I like to be punched in the face with hops/bitterness. I boiled the kit up and steeped a bag of hops for 15mins.
What can I do to make the kit (a) stronger and (b) more hoppy/bitter? Use more hops, boil for longer, dry hop?
I'm fairly new to this brewing lark, but since I obviously have an extreme taste in beers can you offer me any advice about how to get what I want? I'm mainly homebrewing for economical reasons, and moving to full/partial mash not only scares me but does not seem that cost effective so would like to stick with a kit for now. Ideally I'm just looking for something that is around the 6% mark with a lip-smacking level of bitterness/hops. Advice please?