You need to set a right-align tab stop for the TOC entries that is the same width as a single column. (Or switch to a right-align tab.)
Edit: I meant switch to a right-indent tab.
Barb's right but for TOC's like yours I find it's easier to use the Align Right tab instead of a standard tab stop. You can do this manually by pressing Shift + tab on your keyboard but if you're using the TOC feature in InDesign, simply replece the default tab characer (^t) with (^y). This is a lot more flexible because if you ever change the frame or column width, the tabs will still align to the right side of the frame/column.
Thanks, will give it a try.