Bootstrap columns have 15px of padding and the version of bootstrap you are using has utility classes that let you modify the amount of padding.
p-0 means 0 padding, so you could use that instead of adding a negative margin.
Your HTML would be like this instead:
<div class="col-lg-6 p-0">
You’re off to a good start - try to let bootstrap do the work for you as you get more comfortable with HTML/CSS, otherwise, things can end up causing conflicts and getting complicated to debug