Derailleur Damage

Oh balls do you need to take it to a mechanic - I say that as an ex-mechanic myself. If you can't get it right by eye, the tool is easy enough to make. £2 in materials + half an hour of your time beats £20 labour charge and an afternoon waiting to get your bike back.

How the crap are you gonna make a derailleur hanger alignment tool in half an hour and with £2 of materials?

If that came into my workshop I'd most likely do it there and then because it's a 5 minute job and I'd probably do it for a donation to the cake/beer fund, not £20.