Yes, both of mine developed a lump after their first shots; it scared me at the time, but luckily I discovered them just before their next vet visit and they said it's very, very common. They also told me the lumps should disappear over a couple of weeks, which is exactly what happened
Unless you're really worried, perhaps keep an eye on the lump for the two weeks until the appointment - by which time it will probably have gone anyway
Dsis had kittens who both had a lump appear after their jabs - it's not uncommon and nothing to worry about, just keep an eye on them. Mention it to the vets when you go back, especially if it's still there, but it's most likely nothing to worry about.
However if it gets any bigger, or the kitten's behaviour changes, then definitely take them to the vet straight away.
Thank you for your help! I think I'll keep a watch & wait approach, but may ring the vet just for some further reassurance. Little kitten seems fine, eating lots, having mad bursts of energy where she swings from curtains & attacks everything, and is very affectionate. It just seems like a big lump for a little kitten.