Working out at 7 weeks

So I was invited to do a work out class with my boss for tomorrow night and she has been begging me to go with her but she doesn’t know I’m pregnant, and I don’t want her to know yet because we told way too many people last time and I had a miscarriage in November. Anyways, my question is, what is the rule anyways in regards to working out or lifting a certain amount? Are there restrictions in the 1st trimester? I usually only walk the dogs, I don’t work out a lot, but I’d like to start doing some working out here and there. I just don’t want to do anything to harm the baby!