asalamalaykum everyone
my question is about ghusl
1: i suffer for waswasah alot generally, and after performing ghusl, i start having doubts about wether i washed every part perfectley or not, i generally spend alot of time under the shower while perfroming ghusl, so i am fairly certain that water gets to every part, but i doubt wether i scrubbed every part of my body with water, and this causes me to then perform ghusl again the next day or later in the day because of these doubts.
2: its not possible for the hands to reach every part of the back while doing ghusl, so i just make sure the the shower water reches the back, and scrub the parts of the back i can reach, is this fine?
please answer both parts of my question