I'm currently unfit and cant run past 3/4 of a mile.
Well, you made that mistake and it's water under the bridge at this point. You can only start from today, and work a plan to get fit. Actually your cadre will put you on remedial (usually means an extra day of PT compared to everyone else). Your cadre won't care about your past mistake of arriving out of shape so long as you give every effort to follow their remediation program. An trust me, you WILL pass APFT if you give it just 30 minutes a day of effort.
don't think I can handle being a scholarship student my freshmen year.
Sure you can. It will be tough, you will feel like giving up most days, but this is where you start to define the rest of your life. Are you a person determined to persevere and get through to the other side, or are you a quitter? You only THINK you can't do it, but there is nothing in ROTC that 90% of the population cannot do. You just have to want to.
how can I give up my 3-year AD scholarship and be able to attain a 3year normal scholarship next year or get a 2-year scholarship?
99% no. If you give it up, why would the cadre, assuming they even get a scholarship for use as 3 yr in-college, give it to a problem cadet? You can probably get approved for Advance Course assuming you give up your Scholly, but continue in the program and pass class, lab, and APFT, but then what' the point of giving it up now?
I would like to remain in ROTC for 4 years, I just don't know what to do about my scholarship and the extra work I have to do because of it
You have to do the extra work to stay in ROTC without a scholarship also. YOu won't be approved to go on to Advance Course (years 3 and 4) if you haven't done well in years 1 and 2.
Bottom line, most cadets feel overwhelmed, homesick, and depressed at times as freshmen away from home. You WILL get over this, and you will thrive. Just give it time and effort.