If my parents aren't going to help me take care of my turtle, is it okay if I take care of it myself?

It sounds like your parents used to help and are stopping now that you're older? If that's true, it's probably overwhelming for you right now, but you can do it. DO NOT whine that it's too hard; if they haven't already, they will suggest selling it. You could ask that they stand by and watch you do everything for the first few times; that way they are there if you have problems and you will feel more confident, but you are the one doing the work. Get a calendar if you don't have one to mark down dates you need to do certain tasks. If you want to enjoy the benefits of having this pet, you need to take the responsibility for taking care of it. It's hard to be responsible, but if you are 11 years old, you are old enough to clean a tank and change the water. My daughter took care of her own fish when she was 8.