How do i align the page numbers in a toc to left in Pages?
I'm not sure, but it seems as though you used Pages' built in Table of Contents feature to automate the formatting. It appears that the special indent settings were accidentally removed, but luckily it is not hard to put them back. 

If you did use the built in tool, it should be very easy to fix. Click anywhere within the region of the table of contents (this will select the object). Then click on the ruler to create the special indent setting that will control where the page numbers will go. That should do the trick!

If you ever would like to delete the indent settings, all you have to do is click on the blue triangle representing the setting you would like to remove and drag it out of the ruler and let go of the mouse. Here is an example screenshot of the ruler with indent settings and a table of contents: