my car failed the mot on the exhaust emission test the readings are as follows its been cheked twice

first idle test

engine speed 2750-3250 rpm not checked

co max 0.30% reading was 0.39% 1st time 2nd time it was 0.46%

hc max 200 ppm reading was 57ppm 1st time 2nd time was 64 ppm

lambda 0.97-1.03 reading for both was 1.02

second fast idle test

engin speed not checked

co max 0.30% reading was 0.32 1st time 2nd time was 0.35%

hc max 200 ppm reading was 26 ppm 1st time 2nd time was 41ppm

lambda 0.97-1.03 reading was 1.01 1st time 2nd time was 1.00

natural idle speed

engine speed not checked

co max 0.50% reading was 0.29% 1st time 2nd time was 0.46%

changed mid and backbox last week sealed all joints no leeks forgot to re connect sensor befor the first test reconeckted for second test and failed with higher co could anyone help me as i do not have alot of cash to spend on getting lots of parts