Here's a good motivational video for you:
[youtube]http://www.youtube.com/watch?v=_tjYoKCBYag[/youtube]
Grades are at least as much hard work and jumping through hoops as they are aptitude and intelligence.
About 10 years ago I failed out of college, with one D- and the rest straight F's. I've got excellent test scores, and could have gotten straight A's, if I had done the work. I didn't do the work.
I'm finishing up the first semester at a different college, now, and athough grades haven't been posted yet, I've done the math on what my grades should be, and I'm looking at 2 A's, an A-, and something in the A-C range. I probably should have done better, but I did alright, because I did the work.
This first semester for me was, coincidentally, 13 hours of all easy courses. The combination of a light schedule and easy classes was actually a little boring. So don't let boredom get the best of you. Given what you've said so far, I think if you do your best you can get straight A's or nearly straight A's with a 13 hour/easy class schedule.
Show up to every class. Do every assignment. Study for every test.
I'd say "Good Luck", but I don't think luck will end up having anything to do with it.
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"A dead thing can go with the stream, but only a living thing can go against it." --G. K. Chesterton