If your logo looks too small, you could try cropping it in tighter.
The easiest way to do this is to simply screenshot the logo cropped in close to the logo itself, without unnecessary white space around it.
Additionally, keep in mind that Safari Portal is optimized for rectangular-shaped logos. If your logo is circular or square, cropping it in tight can help it better fit the template. You can also try using the itinerary template with more space for bigger logos.