Old solder doesn't work as well as the fresh stuff. It's super easy to add a dab of fresh solder, don't worry too much about it.Don't, like, HEAP it on!
That's . . . quite a large blob. At least it is nice and symmetrical, I've seen some first attempts that looked like a solder explosion, with the stuff everywhere. If you just use less than what you used there you should do fine.
let's see some pics of that mod!