"Assisting my grandmother" - COMMON APP. extracurricular activities question

Hello, this is my response to the question. My problem is it's too long, it's 307 words. If someone could help me edit it I would highly appreciate it!! Thanks!!

Please briefly elaborate on one of your extracurricular activities or work experiences in the space below (150 words or fewer, 1000 character maximum).

From a young age, I always believed it was crucial for me to assist my grandmother with household obligations. I started watching over my sister before and after school when my grandmother felt I was old enough, I made sure my chores got done and would start cooking dinner. My grandfather was a hard working man and drove a truck for a living; he is my inspiration for being a diligent worker. I started working when I was 15. I was hired to work at Quick Chek in October of 2005 and have been working there since. I currently hold the title as a Shift Leader, which means I am responsible for making sure everything is completed on the shift I am working and everything is handled in a way to our company's standards. I was offered the title of assistant food service manager; however, I had to decline because the position would require me to work more hours; being a full time student I felt my education would suffer, thus I declined. Though I still assist in other ways, I aid the food service manager with coming up with new cost-efficient techniques to improve our store's expenditures and receive small awards as recognition. I have also assisted my store leader by giving insightful input on various store affairs; for example, I developed new questions to be used in parts of the interview process and enhanced floor display plans. The classes I have taken so far have taken my natural instinct to be diligent to a new advanced level. The knowledge I've absorbed from my classes in marketing and business has led me to advance in my first job further then I ever believed I would get. I look forward to increasing my knowledge and furthering my career advancements through a rewarding education at your reputable institute.

Here is a run on sentence:
I started watching over my sister before and after school when my grandmother felt I was old enough, and I made sure my chores got done and would start while cooking dinner. ---I added the word "while" to make it clearer. Does that seem okay?

hyphen: hard-working

This essay is very good! I think it gets better and better as I read. At the end, it is very strong because of the examples from your work, and I want to suggest also getting more detailed about your professional goals (i.e. what topics you are learning now in your independent reading, and what specialization best suits you...)

:-)