Okay so I started highschool, and it's great! I have friends in my periods and during lunch, and the building is AMAZING! But there's this dude that I've known since middle school. I used to beat him up A LOT (mainly because he's an anmoying twat that trolls a lot). So anyways, we made up and became friends long ago, but now he likes me! I hate to admit that they're dates, but yeah, we already went on 3. And he asked me out to our High school coronation! I turned him down though, and now I don't know what to do! I'm only a freshman,and I'm trying REALLY hard to get better grades since all my life I've been a straight C student. Does anyone have any advice? Because as great as a relationship sounds, it's a bit scary when you think about it, and I don't need another weight.

This might not be the best time for a relationship if you realy need to get better grades, and it sounds like there are other things going on, too. But if you think you can balance it out, it might be okay. Just don't let anything become more of a promblem than it needs to be.

You should just tell him your not ready for a relationship if he really cares about you he will understand.

Just because you are in a relationship it does mean you won't get good grades... and vice versa.
To have good grades you need to study, to pay attention in class, to dedicate your mind to your duties as a student. As long as you do that, how you spend your free time, is up to you. You can also study with him... why not.
The best example I can give you are 2 colleges of mine, from those times of school. They started dating at the age of 17, now they are married, one is a Medic and the other a Pharmacist. Those 2 professions req the highest grades in my country, 19 out of 20 and 17 out of 20.
Yes they spent many ours studding, yes there was little time to play around, but they were still going out every now and then, having fun like every one else.
They were just mature enough to say, we want to follow this path and this will only work if we help each other, finding ways to stay close, without compromising our duties.

Both options are ok, stay with him or push him away, it is up to you. Just take a decision you wont regret latter.

Honestly I told my friend that wanted to date me, "No way I'll never go out with you, you're too immature for me." Idk if you want to say that but he wasn't really bothered by it but just stays by my side as a friend. He does try convincing me and I still say no. I knew him in middle school too and still know him in college 2nd yr. My point is I don't feel right about dating a brat and can do better. Maybe you can too and I wasn't a straight A's person until high school studying a lot. Maybe you should focus too.

Would you prefer a life where you would feel uncertain about what is going to happen tomorrow or a life where you know that no matter what happens in your future relationships, you are not going to be in a financial crisis or even jobless? Well, the uncertain future sounds like fun but this is up to you to take the right choice.

Minna... arigatou...

Just think about what your priorities are. I've started high school and I'm thinking exactly the same as you. Some guy that sits next to me in homeroom asked me out to the first dance of the year and I said no, because I don't want anyone to like me and I'm not trying to like anyone. Later on when I'm able to handle all the weight I have on me, I'll think about love. So I guess if you go by my guidelines, just think about love when you know you can balance everything out.