Nothing wrong with strength and power. Aikido is about efficiency - using power without resistance. Thus you need to gently unbalance someone with perfect timing, then, when they can't resist, grind them into the mat.
Unfortunately in normal training this is not acceptable, since uke needs to be able to survive. Thus, do not feel that you have to be 'gentle' but realise that
i. you must not damage people
ii. that the hardest part of aikido is using timing and sensetivety correctly to unbalance your opponent
Many people may be intimidated by your size. I would advise against being over gentle - you should be relaxed but use appropriate force where necessary and when there is no ability for uke to resist. However just being 'soft' is teaching your body to do aikido in a completely incorrect way. Possibly train with larger uke if you find it difficult training with little people until you feel more confident in your technique.
My apologies to all - didn't read other posts fully.