Another beginner guitarist question..?

So I just got my first guitar (fender acoustic) 4 days ago, and I've been playing it for AT LEAST 3 hours a day. So far, I've attempted to learn the intros to: "Welcome to My Nightmare" (Cooper), "Angry Chair" (Alice In Chains), "Everlong" (Foos), "Day Tripper" (Beatles), "Smoke On the Water" (Deep Purple), "Big Me" (Foos), "About a Girl" (Nirvana), and "The Pretender" (Foos). The only ones I can actually play decently are "About a Girl", "The Pretender" (sorta), and "Smoke On the Water".. These are such SIMPLE songs! I just can't get the chords to switch fast enough, but it seems like I practice SO much and it's just very frustrating. Am I putting too much pressure on myself? By the way, I'm 17 and hoping to become a very good guitarist some day. ANY opinions and advice at all is greatly appreciated. Thanks!