I'm not that interested with the rest of the computer except the graphic card so I was wondering is it necessary to absorb everything in computer engineering or if I should go for something else such as electrical or electronic engineering.
Also would "Engineering Technology" be better?
I'd say EE with a minor in CS and maybe physics (and obviously take the highest math courses possible) would open the world to you, if you're competent enough for it. You'd want at least a master's degree, maybe a PhD at some point. GPU design (any design, really) isn't a one-person job. You'll likely be on a team responsible for one specific area (architecture, software, fab, board layout, testing) rather than the whole product. There's also the mechanical side (packaging, thermal design), or manufacturing.
Stay away from engineering technology if you want to do any real, complex design work. I got a BS in EET (4-year degree with two co-ops) and while I'm in a design/R&D position, I'm more on the development and verification side of things. I've designed boards from schematics to finished PCBs, and had a heavy hand in kW-scale system design, but not having the full math background is somewhat of a disadvantage. If you go to a good school, you learn nearly all the same things as a regular EE, but the classes are watered down with algebraic (calc 1/2-level in the higher courses) equations. Sometimes I wish I had gone with a real EE degree, but I love being more hands-on and in the lab. Luckily in my position, I have a good mix of design and hands-on work, and I've learned a lot on the job.
Either way, you really have to push yourself.