If you want to get stronger the only way to do it is to challenge yourself. You're not going to get strong sitting around all day. You're not going to get strong watching tv. You're not going to get strong just joining a gym. You're not going to get strong by joining a gym that doesn't like people who want to get strong.
Gaining strength takes work. It takes dedication. It is a huge part of being fit. What good is it if you look good but can't shovel snow because you're not strong enough to lift the shovel. You need to challenge yourself. Get off that machine and pick up a dumbbell, barbell, kettlebell, or even some kind if suspension trainer. How about doing some push ups? You need to be strong to move your own body weight. If you need to let out a grunt because it takes effort feel free. I won't judge. This is a real judgement free zone.
This is the time to get strong and stay strong. It doesn't matter who you are, you can always get stronger. Exceed you're limits. Go a little to far but be safe.