The price of a gallon of gas in Maine is rising, but not as fast as prices are going up nationally. Price-monitoring website MaineGasPrices.com reports Monday that the average retail price of a gallon of gas in Maine has risen more than 3 cents in the past week to $3.55. That compares to the national average that has jumped almost 9 cents per gallon in a week to an average of $3.67. In-state prices are now 21 cents per gallon lower than at the same time last year and a little more than a penny higher than a month ago. The averages are based on a survey of more than 1,200 Maine gas stations.