The problem is not where people are trained, but how they are trained. To complete a PPL in 3 weeks is pushing it even for the most able student. Inevitably, you will have been on the edge of your ability most of the time, some people learn well under pressure, some do not.
Now that you have your licence you need to consolodate what you have already learned. If your are SAFE, you will be able to solo quite quickly after a check out, maybe a couple of hours. If you need additional training it may take longer, I have seen some new PPL holders take up to 15 hours to be sent solo. Remember some schools are anti US training , after all their livelyhood is at stake. Even if you change schools or clubs in the UK the new club will not know you, and require a thorough check-out before they let you hire their aircraft.
Training in the US is different, some schools may want to retrain you in the UK way, that can increase the time it will take. However long it takes, it is still flying, and you will learn from the experience hopefully, to make you a safer pilot.