If your prints are too dark than you are either exposing your paper too long or developing them to long.
Not sure why your print is coming out darker than the exposure and development you determine by your test strip but something is going wrong.
Personally I always developed my black & white prints by observation. I would put a small square of paper exposed and developed to D-max in the tray then watch the print develop under the safety light comparing the darkest areas to my piece of black paper and when I saw solid blacks in the darkest parts of the print I quickly transfered it to the stop bath. This is decidedly low tech but almost every print came out this way.
Do you develop the pictures yourself? You may be using too much or too little of the solutions.
It takes practice to know the proper aperture to use. What I learned when I was learning photography in college is that we should 'bracket' our shots when we first start out taking photos. Bracketing means taking a photo with your determined aperture, and then taking the same shot one F-stop higher, and another one one F-stop lower. Then by looking at your results, you start to get an idea of which F-stop should be used in certain situations.
Here is a helpful guide:
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