(1) You could have negotiated a different join at Lydd. You can always try negotiating a different join. Plain English will do: "unable to join overhead at 1,500' due to cloud base, request right base join at 1,000' [or whatever]".
(2) I write three altitudes down on my PLOG, not just one. One is the maximum possible altitude, taking account of controlled airspace. One is the lowest I'll feel comfortable going down to (usually simply 1,000' above the number in the square on the chart, but it depends on the location and your club rules may be different). The third is the planned altitude, the one I've looked up the forecast wind for and done the sums for. I don't worry about being unable to continue at the planned altitude as long as I can stay above my minimum.
Having said which everybody else is of course absolutely right - deciding to turn back because you don't like it is never a wrong decision - and you are absolutely right - you don't get sent solo to see if you can find your way to Lydd in perfect weather, you get sent solo to see if you can take the responsibility for making your own decisions.