Praise be to Allah
What the questioner mentions has to do with a kind of waswas (whispers from the shaytan), because purification and prayer are simple matters that do not need such concern. The religion of Allah is easy and there is no hardship in it, as Allah says (interpretation of the meaning):
And the Prophet (peace and blessings of Allah be upon him) said: “The religion is very easy and whoever overburdens himself in his religion will not be able to continue in that way. So you should not be extremists, but try to be near to perfection and receive the glad tidings that you will be rewarded.” Narrated by al-Bukhari (39).
The remedy for what you are suffering involves three things:
1- Constantly persisting in remembering Allah, may He be exalted.
2- Turning to Him and asking Him for healing and recovery from this problem.
3- Turning away completely from that which the waswas is calling you to do. So when you have relieved yourself and washed yourself (istinja), get up and do not pay any attention to whether your hand touched a tahir (pure) place after touching the najasah (impurity), or that drops of the istinja water landed on your feet or body, because the basic principle is that things remain tahir, and uncertainty as to whether your body or clothes have become impure does not have any effect. You should understand that your body and clothes, the place where you pray, and other things are pure and continue to be regarded as pure unless we are certain that they have become impure. As for doubts, imagination and waswas, no attention should be paid to them. See the answers to questions no. 62839 and 25778.
Purification and removal of impurity is done by washing the private part; it is not essential to wash the area around it, so do not pay any attention to the water that drops elsewhere, as stated above. Be confident that you are tahir, praise be to Allah, and that your prayer offered with this purification is valid and accepted, if Allah wills, for Allah is Most Merciful and Kind, and He shows mercy to His sinful slaves, so how about those who are obedient and love Him?
With regard to deciding to stop wudu or prayer, that does not matter either, rather you should ignore these thoughts and carry on with your wudu or prayer, because there is no reason to interrupt an act of worship, rather this is waswas and it does not affect your act of worship, praise be to Allah. No matter what thoughts of interrupting your act of worship or repeating it come to you, do not pay any attention to that, and carry on with it, and ask Allah to accept it, because you have done as much as you could, and you have done what was required of you, and Allah does not burden any person beyond his scope.
Remember this advice, and carry on, and ignore the waswas, for it is a trick of the shaytan, but his tricks are weak as our Lord has told us. Be confident that if you ignore the waswas it will disappear, by the power of Allah.
We ask Allah to help you to obey Him and to make you happy by worshipping Him, and to take away the problem that you are facing.
And Allah knows best.