I wasn't too sure which topic area to post this...
On my older lcd watches, I always cut a piece of clear mobile phone screen protector to the size of the watch glass and apply it to the watch. Every single time I do it though, at least one edge has a bit of non contact (looks a bit like minor bubbling at the edge). It looks good as is, it just bothers me that it's not perfect lol. I use a craft blade to cut the stuff.
What is the best easily available clear material to use to protect watch glass?
Thanks in advance all.

Edit: I forgot to mention I have tried several different brands of phone screen protectors, all give slightly imperfect results.