The Ultra VS Mono debate has been done to death so anyone wanting to read them just do a search, there are bunches of them.
Like Joe mentioned I would iron down the edges good but I wouldn't try a heat gun just yet. Mono can over heat before shrinking and seperate and or pop a hole in it. I would heat my iron up real hot and just run it over the sags and wrinkles without touching the covering with the iron. Mono goes on at a much higher heat then Ultra and doesn't always shrink as well so you may have to keep adding higher temps to the iron until it starts shrinking. If all else fails then you go to the gun but be ready to watch the covering pull away from the edges if you over heat it.