Not a bad start having a level or plumbob should some troubleshooting be nessecairy,
but as above a cheap 150mm engineers square if it wouldn't be too large to fit under guides, can be bought for a tenner at axi.
Make sure the blade is properly tensioned before trying.
Might need a washer under there or what have you.
This is an opportunity for both leafs to become un flush, so some biscuit tin might be worth having at hand should you need to do that also.
Good luck