Dynamic SQL Colunms Into Rows

Im trying to write a SQL script that will turn the rows from one table into colunms. I'm using the sp_excutesql porceure and it keeps coming back with an error.

The problem is that i cant seem to be able to use @parameter as a name when i try to dynamically create a column. Its a dynamic sql problem but i cant seem to get around it.

This is the problem line -- SELECT @SQL = 'ALTER TABLE tblHM21 ADD @ColName  varchar(50)'
Create Table tblHM21 (

uidHM21 uniqueidentifier

);

-- loop through tests to get bring back names of the rows
--
--
declare @rowCount int
declare @i int
set @i = 1


set @rowCount = (SELECT Count(intTestTableRow) FROM tblHSTests)

while @i <= @rowCountBegin
declare @ColumnName nvarchar(50)
set @columnName = (Select strTestName from tblHStests where intTestTableRow = @i)

declare @SQL nvarchar(500)
declare @params nvarchar(4000)

SELECT @SQL = 'ALTER TABLE tblHM21 ADD @ColName varchar(50)'
SELECT @params = N'@ColName nvarchar(50)'

EXEC sp_executesql @SQL, @params, @ColumnName


print @i
print @ColumnName
set @i = @i+1
End

select * from tblHM21

Drop Table tblHM21