Married Joint. Employer puts $1300 in HSA annually. I put $200/mo after tax. My W2 states $3700 from employer cont. Shouldn't the employer portion be $1300?

The total $3700 is correct as shown on your W-2, Box 12, with Code W.

Employer contributions to a HSA are not considered income and are not subject to income tax or payroll tax. Since you, as the employee, also paid via a salary reduction arrangement, those contributions are also considered employer contributions.  This means they're not subject to income tax or payroll tax. 

Follow this link for a more detailed description: Employer vs. Employee HSA contributions.