I preheated the oven and then set the cake in there.. Set the timer and went about my routine.. when the timer went off (35 minutes later) the oven wasn't on..

I turned it on.. will my cake be alright?

it is a scratch white cake. no baking soda

Welcome to the wonderful world of baking! We have all done this at least once...at least I have.

Yes, it should be ok. Just take the cake out why it is pre-heating, then put it back in.

Good luck.

I've done it too! No harm done. Just bake it.