EF-S 55-250mm f/4.0-5.6 IS II Telephoto Zoom

I'm sure some of you know my ongoing saga with trying to do intimate indoor med/low light portraits/body shots in a small room.... I just finally got a great deal on the Ti3, + the default 18-55 + Tiffen 58mm UV Protection Filter + EF-S 55-250mm f/4.0-5.6 IS II for $570. It was a package deal so my question is, should I keep and use the 55-250 for my project and more, or should I flip it and try to get something else more useful to me? I heard it is bad for sports and is a bit soft on the 250 end (which kinda sucks for a zoom lens I guess) and soft on the edges on all lengths, but right now all I care about are my portraits so...

If I should flip it, what else within a $100 price range of the 55-250 should I get that will do me a lot better? If I can I would love to keep a zoom lens to make life easier, but if you really think there is a fixed lens out there that will do a whole lot better for the price for my purpose, please advice... but please keep in mind my MAX shoot distance is about 7-8 ft. Thanks!