It is not normal for a cooktop to have a gap in the center front when resting flat on the counter. This may be an issue with the installation or the cooktop itself. You should contact GE Monogram customer service for assistance in resolving the issue. They may recommend a fix or arrange for a technician to come and inspect the cooktop. Also, Keep the original packing material and the installation instructions, in case the cooktop needs to be shipped back for service.
If the issue is related to installation, a DIYer with the proper tools and knowledge may be able to fix it. However, if the issue is with the cooktop itself, it may require a professional technician with specialized training and equipment to fix it.
It's recommended that you consult the manufacturer's installation instructions and troubleshoot the issue, if you feel comfortable doing so. If you are unsure of your ability to fix the problem or if the problem persists, it would be best to contact the manufacturer or a professional appliance repair technician for assistance.