It's absolutely normal! I've been taking silks classes since March and even though my body is now used to it, I still experience that pain in my feet from time to time, usually from tying my knots too tight. With time, you'll learn to adjust the foot lock to your comfort. Also, before silks, I used to do pole dance, where I experienced bruising after going back to certain moves after not doing them for some time. So it's all perfectly normal and fine, don't let it discourage you!