Your levels are supposed to approximately double every two days. So, 450 at 4w - you would expect in the range of 900 at 4w2d 1800 at 4w4d, 3600 4w6d, etc. Your levels are on the higher side but not significantly; probably doesn't indicate much except that your pregnancy is progressing as it should be for now - congrats!
Married Sept '13 TTC Dec '13 BFP 10/8/2014 MMC 11/20/2014 D&C 11/26/14 BFP 9/20/2015 MMC 10/7/2015 D&C 10/15/15
Re: High beta?
Betas don't generally twins or not. Wait until your first ultrasound.
DD1 born 11/2014
DD2 born 6/2016
Married Sept '13
TTC Dec '13
BFP 10/8/2014 MMC 11/20/2014 D&C 11/26/14
BFP 9/20/2015 MMC 10/7/2015 D&C 10/15/15