I think you have bits of 2 or 3 things rolled up together:
1. Your Max State Pension would be £155 or whatever if you had paid full NI for your whole career. Because we had a pension scheme which was contracted out we get less than those that paid the full stamp - so I suppose if you pay a full stamp for another 10 years it would boost your State Pension - you need to get a quote from them as to how much you pay in and how much you will get in 2025 and do the sums.
2. RE your RAF (or other Public Sector Pension) being reduced when you start to receive the State Pension - see the thread "Service Pension Reduction" This will explain about the GMP - it hit me last year when I started receiving my State Pension.
whatever, retirement is still good!!