Changed brake pads now car acts like it doesnt want to stop completely

I changed one brake pads of the left front tire .. Thought they needed change but took wheel off theyre basically new. Thing is everything behind wheels upfront are all rusted.. Mainly everything. Brake light isnt on but ever since we put the new pads on that one tire the car acts like it doesnt want to stop at a stop light or stop signs then makes a grinding noise too.. Takes alot of pressure to press on brakes. I dont want to bleed brakes because i dont want to break anything. I need to know if i have to get anything replaced? Is it serious? Or am i just over reacting .. I need someones help because i know nothing about cars and dont want a shop to tax the hell out of me because im a female and know nothing about cars.. Please anything will help