I'm a 16 year old girl and I checked my blood sugar and it was at 125 and the day before it was as 135 is this bad should I be worried?

Blood sugar. Was it fasting or random sugar?normal fasting sugar is less than 100. Sugar after meal may vary depending on what you eat.
Probably fine. if they were fasting levels, that is obtained after 8 hrs of not eating, then they were a bit elevated. if they were obtained randomly, then they are fine. If you are very concerned, check with your doctor and additional fasting tess can be done.