Hey Arafat - cleaning can be frustrating! Just remember to take your time and be gentle. The shower wand can do an ok job, but I found that soaking in a bath for 15 to 20 minutes not only helps with healing, and it also helps get those stubborn bits of fecal matter loose, which makes them easier to remove with a wet baby wipe after the bath. If you spread your butt while laying in the tub, the warm water has an opportunity to swish in the area too. Cleaning will get easier when the swelling goes down in a few days, so hang in there!
The fistula wound will likely look raw and bloody for a while - mine did for about a month. With wide wounds like that, it will take a while for the area to epithelialize. You want the wound to heal from the bottom of the wound bed, and not along the top, which can just form another 'tunnel' (which would just be a new fistula). Try not to worry too much about the wound looking raw - that's normal. I know it sounds a bit strange, but you don't want that wound to heal
too quickly from the top down.
The challenge now is being patient, my friend. Doctors very often underestimate healing time. I definitely understand that you just want all this over with, but the healing (and cleaning!) process will take a while. I really learned a lot from my ordeal -- namely, what I high-strung, hyper-active person I was!

This is the time to slooooowwww down a bit and focus on looking after yourself. The wound will
look scary for a while - possibly a month or more. But it will likely look worse than it is while it's healing. Pain matters as much, and sometimes more than, how the wound looks - if you don't have pain, and the wound doesn't look angry and red, then I'd say you're doing good.
Of course, all this comes from my own experience, so all I say must be taken with a grain of salt. I'm sure your doc will give you some good insights when you have your follow-up on Sunday, which I hope goes really well. :D
You're doing great, Arafat - remember that. Good BMs are really important. The cleaning will get easier, and the scary wound looks worse than it is.