I'm about halfway through my first semester at college.
I'm a little worried about making friends,
You'll make tons of friends. Especially right at the beginning, most people don't know anybody and everybody wants to make friends, so just be friendly and talk to people. One tip if you live at school: Keep your door open. You can get to know a lot of people in your dorm neighborhood this way, which I find very valuable. It's how I met my girlfriend, in fact.
You should also join at least one club. Instant friends really unless you're a big jerk of some kind.
And if you are one of those, you can always join a frat.
(small joke)
keeping up with my schoolwork,
Some people said cut back on video games, which is definitely going to help. I also recommend you cut back on your internet time. This is only the 2nd or 3rd post I've made in the past 2 months, which is huge considering how much I posted all last summer and when I was in high school.
I also suggest you do as much of your work as possible in the library. I find there are far too many distractions in the dorm to get things done efficiently. Going somewhere quiet by myself lets me focus a whole lot better.
How much of a problem this is depends on a lot of things. What kind of food you can get, what kind of gym they have, etc. I've lost weight since I've been here but I don't go to the gym or eat very healthily. I don't snack as much as I used to and do a lot more walking though. What happens to some people is that they come into college having played a sport in high school that they don't continue with (college sports are a humongous commitment btw, a lot different from high school unless you do intramurals or club sports).
managing the new independence, etc.
There's a lotta new independence. You can basically do whatever the eff you want. It ties in with every one of your other worries too. Some kids go crazy and screw things up for themselves. I know very smart people here who probably aren't going to pass classes this semester because they goofed off too much. So try not to do that.
That being said, hell, it's tons of fun being on your own and doing whatever the eff you want. Just have some priorities and self control most of the time and you'll be fine. I personally find time management easier here than it was in high school. WAY less time in class, and I'm already falling into a pretty solid groove.
Best of luck, hope you won't need it!