You've only got three choices here
1) Drive to kwikfit or motasave or whatever is near you and friendly - ask them to just rattle the nuts on, takes literally 8 seconds and they'll do it for a bit of beer money
2) Drive to toolstation like I did and fork out £110 on a cordless impact gun, rattle them on yourself
3) Take them off again, clean the hell out of the nut and the thread with some wire wool/wire brush, put some oil on the thread, put the nut on and then put a hex key in the top of the strut to stop it turning. Tighten the nut using a swan neck 21mm spanner by hand. When it starts to get tight go back and forward and back and forward, add a bit more oil. Eventually it'll clean the thread up well enough that you can finish it off by hand. But will probably take 20mins