Hi, if you can take a picture of your installation from the side that would be helpful. The easiest way to explain the angle sticker is to put an imaginary line that is parallel to the ground through the recline sticker starting at the narrow point of the indicator and moving towards the wide end of the indicator.
If you have a smart phone with an angle app, or a way to measure the angle, you can measure the angle using the metal bars at the back of the seat. Just place it along the metal, and the angle should be between 30 and 45* for a child who is less than a year old. Children over a year old can sit as upright as 20*. (Measured from vertical.)
If the seat is too upright for your child when it is installed in recline position 3, then you can use a rolled towel or pool noodles to increase the recline provided it stays within the allowed range.