iMac 5K Late 2015 SSD Replacement Troubles with Step 35. Urgent help.

I was following this guide on disassembling my Late 2015 iMac 5k 27".

Reemplazo del circuito SSD del iMac Intel 27" Retina 5K Display

I got to Step 35 to remove the 4 T10 screws. I have the Classic Pro Tech Toolkit (before the revamped one came out) and I was trying to remove the bottom right 7.3 MM T10 screw, but have not been able to give the screwdriver enough torque to get it out. I have tried many many times trying to get this screw out, but it is really in there. I ended up stripping the screw (by using so much force) and ruining the T8 head that came with the toolkit (although it says it's a T10 screw, it's actually a T8 because the T8 fits like a glove).

I am completely lost on what to do. I was trying to disassemble the iMac to fit a blade SSD in there and was not expecting to encounter a problem like this. I use this computer at work so I screwed myself over a little.

If anyone kind enough could please advise me on what I can do to rectify the issue I would sincerely and greatly appreciate it.

Thank you!