If you have to ask, ask. It just shows, that you are not very far on your DO, but you know, where you are.
Otherwise just feel where you belong to and line up in that place. If you miss your place a little bit, it is as good as the first one. It you hit the right place it is probably luck (or you do not need to practise aikido any longer
If you are totally misplace you should humbly accept that you are just a beginner in touching the spirit, regardless of your grading.
Simple hint: Do not line up as the first one, nor as the last one, as there might be no space. Look for someone, who you think of being similar grade as you and sit close to him/her. If the dojo has an order, you are probably not bad, if they don't you cannot be bad either. And if they insist that guests have to stay in the left rear corner, it is not your fault.