What is the ruling regarding the prayers I performed and my entry into the mosque if, after performing ghusl for janabah, I doubted after the ghusl that I had not performed wudu, and then I prayed?

Wudu (ablution) is not a condition for the validity of ghusl (ritual bath) from janabah (state of ritual impurity), rather it is only recommended. It is sufficient in ghusl to make water reach all parts of the body. So, if you make water reach all over your body, your ghusl is valid and sufficient, and you are permitted to enter the mosque.

Regarding prayer after doubting one's wudu: If you are certain that you invalidated your wudu, then you doubt whether you performed wudu or not, then you remain in a state of impurity, as certainty is not removed by doubt.

Therefore, you must repeat the prayers you performed after this doubt, without having certainty that you performed wudu before them, because they were prayed without purification.