Hello @withemilystevens,

To make the logo size larger use below given CSS.

For this go to Admin Panel > Appearance > Customize > Additional CSS and paste below given CSS.

.site-branding img.custom-logo {
    max-height: 100%;
}

Hope this helps.

Thank you.

Regards!!

Hello @withemilystevens,

Glad we could help you.

Let us know if you have any issue further.

Also, we would really appreciate if you could help us by rating our theme by following the link given below:

https://wordpress.org/support/theme/mega-blog/reviews/

Thank you.

Regards!!