An easy way to test your tension is to sew a line on the diaginal of the fabric. then gently tug at the thread line by holding both corners of the fabric. the top or bottom side that breaks is the thread that is too tight.
keep adjusting that tension until neither thread breaks. If neither thread breaks then the tension is good. I never adjust the bobbin tension screw. also it is important to thread your machine with the presser foot up so the thread goes thru the tension disk correctly. If the presser foot is down then the disk is closed and the thread will not get hooked in it completely.