Wrong aperture? Too strong of a flash? Help please

Here are some photos I shot this week with a flash and fisheye. I like them but the highlights are too bright and have no details in them. I want to get the exposure to even out.

Will be continuing to shoot on a Pentax k1000 at a dark venue with flash. My metering is set to the flash sync speed 1/60 at f8. If I shoot at f11 or even f16 would this perhaps be a good alternative to not overexpose the highlights? Keep in mine these shots are set to f8 since the flash is recommending I shoot it at f8. Wondering if my flash is just too strong too maybe, or if I need to bounce the light or try a diffuser on the flash instead. Or if I need to save them as a TIFF file instead of a jpg, to edit them in post production? Have not done that before but is an option from my lab.

All insight is welcome, thank you