Rivets: How to keep them straight? -fursuit sandals

Hi folks, i'm trying to create a large batch of fursuit sandals for every costume I sell, however, this is my first time even touching a rivet gun, rivets or washers.

I've read through tutorials on the net, but i'm very very sad there are no videos for it or photos showing exactly what they mean by
*keeping it straight/keeping the washer on straight or
*how hold your finger on the rivet without pinching yourself and
*how to use the rivet gun (Some of my rivets end up with a huge bloated chunk at the bottom) or
*if i'm supposed to use a washer on BOTH sides of the rivet or just on the fabric side

The holes are only as big as the rivet in diameter itself, I poke them thru without using anything else to create the hole. I think they start to mess up a lot once I try to really push down on the rivet which is impossible to do with one hand and hold it at the same time ;__; It honestly made me resort to using my body weight to get the handles together. Are they bending because the material has the strange oval designs on one side or some other reason?



Yeah.... Please help me. If someone could do a clear-video or HD quality video up close or anything I feel that would be a huge help for new people making sandals.
But if you can be of any help, please provide!

I'm using interlocking foam mats, aluminum 3/16" 5mm rivets with 1/2" grip   and 3/16" washers which fit on nicely.