Tea Ceremony Question

質問があります。

I partook in a tea ceremony today, but it was difficult to kneel on the tatami because I have bad knees. I fell over once (didn't spill anything, though) and apologized profusely.  Is there an easier way to do this?  Is it okay to ask for a chair if kneeling is difficult?  I was offered one and took it, but I don't want to be rude.