Hello new to this posting so excuse any mistakes, I'm building a small single skin extension on the back of my existing garage 3m x 2.5m, it is on a concrete base the problem is its not level, I have started the build on it and I have put 45mm of mortar (mastercrete at a ratio of 4-1) as the first bed at one end of the build, this is my first building project and I am now worried that this is going to be a problem such a large amount of mortar and it may collapse, I now realise I could have put I small slither of a brick in but I have not done this but with it being only 45mm I'm wondering if it was nesscary? Has any body got any thoughts on the matter ? I would prefer not to knock down what I've done and start again.